Discoveries in Australia, Volume 1. / With an Account of the Coasts and Rivers Explored and Surveyed During / The Voyage of H.M.S. Beagle, in the Years 1837-38-39-40-41-42-43. / By Command of the Lords Commissioners of the Admiralty. Also a Narrative / Of Captain Owen Stanley's Visits to the Islands in the Arafura Sea.

by John Lort Stokes

FISHES. PLATE 2. FIGURES 1, 2, 3, 4, 5.
Assiculus punctatus.
Drawn on Stone by W. Mitchell. Hullmandel & Walton Lithographers.

This fish is as thin in the body as a lath, whence the generic name. Its greatest width is at the cheek, as shown by the section figure 3, where the transverse diameter is about half the height. Figure 4 shows the section at the gill cover, and third dorsal spine, where the thickness is less; and figure 5, represents a section behind the ventrals, where the thickness is little more than a tithe of the height, and it gradually decreases to the caudal fin. The oblong profile is highest at the third dorsal spine, whence it descends with a slightly convex curve to the mouth, which is low down--the under jaw when extended, being nearly on a line with the belly. The height of the tail between the vertical fins is equal to half the greatest height of the body. The dorsal and ventral lines are both acute, especially the former, and the medial line of the nape continues acute to the orbits.

The length of the head, measured from the upper jaw, is contained four times and a half in the total length of the fish. The large round eye, situated near the upper profile, fills more than a quarter of this length. The orbit is surrounded by a ring of muciferous canals, with open orifices, which are the only exterior vestiges of the suborbitar chain. The small mouth descends obliquely and scarcely reaches back to the orbit. The intermaxillaries are moderately protractile, but the lower jaw, when depressed, projects still further forward. The maxillary widens towards its lower end, which curves a little forwards. Three pores exist on each limb of the lower jaw.

The teeth of the upper jaw present a fine, but rather uneven and broad cardiform surface at the symphysis, which narrows to a single row towards the corner of the mouth, where they are a little longer and more subulate. Four canine teeth stand across the end of the jaw anterior to the dental plate, the intermediate ones being shorter than the outer ones. The dentition of the under jaw differs in the dental band being narrower, and in there being a conspicuous canine in the middle of each limb of the jaw. There are also six canines standing across the extreme tips of the jaw, opposed to the upper ones. Most of the teeth are slightly curved backwards. The chevron of the vomer projects from the roof of the mouth, and its surface is armed by minute teeth in about three or four densely crowded rows. The palatine teeth are still more minute, and the band is four or five deep. The teeth, when examined with a lens, appear to be very acute and in nowise spherical. The pharyngeal teeth are subulate and acute, and of unequal heights. There seems to be only one inferior pharyngeal bone below; but without dissection this could not be clearly made out. The outer branchial rakers are long.

The narrow, slightly pitted, scaleless disk of the preoperculum bounds the scaly cheek behind and below, and has an entire edge with neither spine nor acute angle at the bend. The other pieces of the gill cover are closely covered with scales, only a little smaller than those of the body. The pretty wide thin inter-operculum lays freely over the gill membranes, and covers them when shut up. The sub-operculum is minutely crenulated on the edge, and has a small sub-membranous tip, which projects a little beyond the three opercular teeth. A small curved notch marks the separation between the interoperculum and sub-operculum.

The scales extend on the crown of the head to the middle of the orbits. The snout, lips, jaws, the place at the corner of the mouth over which the maxillary glides and the gill membrane are scaleless. The scales of the body are very regularly disposed, showing rhomboidal disks when in situ, with strongly ciliated edges. The lateral line ascends at its commencement and bends rather suddenly under the first soft dorsal ray to run near and parallel to the ridge of the back. It terminates beneath the sixth ray from the end of the fin, but recommences on the fourth scale beneath, and runs in the middle height of the tail to the base of the caudal. Two or three of the scales before its recommencement, have a minute pit in the middle of their disks, as is not unusual with the Glyphisodons. The first part of the lateral line forms an almost continuous tubular ridge traced on thirty-eight scales of the second row from the summit of the back; the posterior part traverses six or seven scales. There are twelve or thirteen scales in a vertical row on the side of the body.

The anus, situated a short way before the anal fin, has a very small aperture.

There are no scales on the fin membranes. The three dorsal spines are short, graduated, moderately stout, and pungent. The twenty-three soft rays are all distinctly articulated, and more or less branched. The last ray is divided to the base, and is graduated with the two preceding ones, giving a rounded form to the posterior tip of the fin. The specimen had the anterior part of the fin frayed a little, so that it is probable that the soft rays are higher and less distinctly branched than the artist has represented them to be in copying the example placed before him. The ventrals are in a line with the tip of the gill cover and first soft dorsal ray, and from the extreme narrowness of the pelvis are close to each other. They are tapering, pointed, and overlap the beginning of the anal, which, though it have fewer rays than the dorsal, is similar in structure. The pectoral and caudal are much rounded, especially the latter. There is a greater space between the anal and caudal than between the dorsal and the same fin. In the caudal there are twenty rays, including two very short ones above, and the same number below.

The general colour of the specimen, which has been long in spirits, is shining yellowish-brown with several round dots of azure-blue scattered over the body. The cheek is crossed obliquely by a row of three spots. The figure errs in representing the spots as dispersed over the cheek; they are in fact ranged in a row. Length, 2 1/2 inches.