Colour.—From some well-preserved dryed specimens in Mr. Stutchbury’s possession, it appears that the sack, cirri and trophi, were dark blue, as in I. Cumingii; after being long kept in spirits, these parts become brown.

Generative System.—The penis ([Pl. IV], [fig. 9 a]) is very singular in structure; it is of the ordinary length, but of small diameter; it tapers but little; it consists of a moveable articulated, and a fixed unarticulated portion; this latter is smooth, much flattened, not divided into segments, and projects straight out under the caudal appendages; it is about one third of the length of the entire penis; it corresponds with a part present in all Cirripedes, but here surprisingly elongated. The articulated portion consists of separate segments, twenty in number, quite as distinct as those of the cirri; each one is oblong, being longer by about a third part than broad; each has a few short bristles round its upper margin; the terminal segment has a circular brush of bristles. The vesiculæ seminales are easily seen, though they are narrow; they are slightly tortuous; they enter the prosoma, and lie on each side of the stomach; their outer case has a ringed structure, but is not fibrous; the contents in the best specimen consisted of a mass of spermatozoa, which I saw with perfect distinctness. The testes are unusually large and egg-shaped.

Ova, spherical, 5/400ths of an inch in diameter, united as usual into two ovigerous lamellæ. The ovigerous fræna are extraordinarily small, and might be very easily overlooked; their length, in a full-sized specimen, was only 7/400ths of an inch, and they projected only 2/400ths from the inner surface of the sack. The glands on their margin, to which the lamellæ adhere, are pointed oval, with an extremely short footstalk, and that rather thick; the entire length of gland and footstalk, being only 2/3000ths of an inch. The larvæ, in their first stage of development, offer the usual characters, and closely resemble those of Scalpellum; the probosciformed mouth, however, is remarkably prominent, and the limbs unusually thick.

Affinities.—This species most closely resembles I. Cumingii, and cannot be distinguished externally, except by the absence of the blue colour on the marginal and interior portions of the valves; and this can hardly be ascertained without separating and cleaning them, owing to the blueness of the underlying corium. Internally some slight differences may be perceived in the form of the valves. Considering these so slight differences, it is highly remarkable that this species should be hermaphrodite, whilst I. Cumingii is unisexual. There is a greater, though still slight, difference in the included animal’s body; the palpi in I. quadrivalvis are blunter, the mandibles smoother, the olfactory orifices darker-coloured; the rami of the first cirrus more unequal, the spines more numerous on the segments of the posterior cirri, and lastly and most conspicuously, the caudal appendages are very much longer relatively to the length of the sixth cirrus, than in [Ibla Cumingii].

COMPLEMENTAL MALE.

I have examined one specimen of the hermaphrodite I. quadrivalvis, preserved in spirits from Kangaroo Island, and one dry from Adelaide, both places in South Australia, and four from an unknown locality, purchased from Mr. Sowerby; and within five out of these six specimens, males were attached. In one of them, two males of different ages were included, one adhering to the peduncle of the other: in I. Cumingii, also, it may be remembered, there was a case of two males parasitic on one female. I may add that I opened another quite young specimen, from Adelaide, not counted with the above, and it was without a male. The males in the five specimens were attached low down, at the rostral end, almost in a horizontal position, stretching across the bottom of the sack; one of them, however, was placed considerably on one side. One individual which I measured, was 16/100ths of an inch in length, and 5/100ths in width in the widest part, namely, about half down the peduncle. I may state, for the sake of comparison, that the hermaphrodite to which this individual was attached, was, including the peduncle and capitulum, one inch in length, that is, six times as long as the male, and one fifth of an inch in width, that is, four times as wide. The above measurements show that the male of this species is rather more than twice as large as that of I. Cumingii. In consequence of this greater size, I dissected, with the utmost care, the one specimen which was excellently preserved in spirits, and found every part, with a few exceptions, so exactly the same as in the male of I. Cumingii, only larger and more conspicuous, that it will be sufficient to indicate the few points of difference.

The most conspicuous difference is, that the oblique fold separating the thorax and peduncle is more plainly developed, projecting at the point corresponding to [h in fig. 1], [Pl. V], 8/1000ths of an inch; in the middle the fold is notched; it can be traced more easily than in I. Cumingii, running beneath and parallel to the basal edge of the mouth, to the ventral margin of the body. In the mouth there is hardly any difference; the maxillæ, however, have two notches even plainer than in the hermaphrodite I. quadrivalvis, or than in the male I. Cumingii, but the depth of such notches is always a variable character; there are also more spines on the edge in the male of the present species, than in I. Cumingii. Both mandibles and maxillæ in the male I. quadrivalvis, are larger than in the male I. Cumingii, to a greater degree than the larger proportional size of the body in the former will account for; and this, likewise, is the case with these same organs in the hermaphrodite I. quadrivalvis compared with the female I. Cumingii. The tubular olfactory orifices are situated in the same peculiar position as in the hermaphrodite, and as in both sexes of I. Cumingii: they are 1/500th of an inch in diameter, and about as thick as one of the lower segments in the rami of the sixth cirrus.

The thorax, as in the male of I. Cumingii, is quite rudimentary, and serves as a mere flap to protect the mouth. In the three specimens carefully examined, the posterior cirri had each only one ramus, whilst the anterior cirri generally had two: in one specimen, one of the rami in the anterior cirrus was formed of five segments, and the other ramus of three segments, both rami being supported on a uni-articulated pedicel; but on the opposite side of the same individual, the anterior cirrus was represented by a mere knob. The longer ramus of the anterior cirrus, in the best-developed individual, barely exceeded in length the mandibles measured along the line of the teeth! In one specimen between the bases of the posterior cirri, there were two perfectly distinct caudal appendages; these, like the cirri, are in a quite rudimentary condition; one was 5/1000ths of an inch in length, and consisted of three segments, the upper edges of which had short spines; the other was shorter, uni-articulated, but spinose. In a second specimen, these appendages were quite aborted. Close under them, on the inside or towards the mouth, (that is, in the normal position,) there was a rudimentary but quite distinct penis, with the apex projecting freely, and with the sides distinguishable from the ventral surface of the thorax, for the length of 1/1000th of an inch: the corium lining this little penis made the terminal orifice plainly visible. The vesiculæ seminales lie in the usual position, and are conspicuous; they are slightly tortuous, with their ends blunt: in the specimen so well preserved in spirits, they were filled with a mass of spermatozoa, perfectly distinct; and the whole cavity of the body was lined with globular and pear-shaped testes. Assuredly there was no vestige of ovarian tubes. From the greater size and excellent preservation of this specimen, which rendered the examination of the generative system so easy, I was able to examine the contents of the stomach, in which I found the delicate epithelial coat, separated as usual, and containing cellular matter, on which the animal had preyed, but the nature of which I was unable to make out. The anus was much plainer than in the male of I. Cumingii. I saw the eye distinctly. I could not distinguish the orifices of the acoustic (?) sacks; and I think I should have seen them, if they had existed.

Prehensile Antennæ.—I examined these in the larvæ presently to be mentioned, and therefore they were in better condition than in the mature animal when cemented. Their total length, measured along the outside, from the basal articulation to the end of the disc, is 32/6000ths or 33/6000ths of an inch—that is, one third longer than in I. Cumingii; whilst the hoof-like disc itself is 8/6000ths, or only 1/6000th of an inch longer than this same part in I. Cumingii: the apex of the disc is downy, or bears some excessively minute spines. The ultimate segment has its end irregularly rounded, with the spines obscurely divided into two groups, the outer group consisting of two or three longer and thinner spines, and the inner group of, as I believe, five rather shorter spines: the longer spines equal in length the whole ultimate segment. I could not perceive that they were plumose, as in many other genera. A single, rather thicker and long spine, pointing backwards, is attached to the under side of the disc, nearly opposite to the point where the ultimate segment is articulated on the upper convex surface. Another single, curved spine is attached on the outer side of the basal segment, near its distal end.

Development of the Male.—In the specimen before alluded to, which included two males, one of these was only the 30/1000ths of an inch in length, and therefore between one fifth and one sixth of the size of the mature male. It had, probably, undergone only one exuviation since its metamorphosis, for the larva is nearly as long, namely, 25/1000ths of an inch. In this young male, the mouth formed one third of the entire length: it was attached, not as in every other case to the sack of the hermaphrodite, but low down to the peduncle of the other male.