Var. (9), Pl. [14], fig. [6 s] [C. spinulosa, of Leach (!)]—Hab. Unknown.—The shell is undistinguishable by a single character from many specimens of the first, third, and fourth varieties; it is not permeated by pores. The scutum and tergum, with the exception of the one striking difference of their being calcified together without any trace of a suture, are identical with those of var. 3, as may be seen by comparing the figures [6 h] and [6 s]. Hence to separate this form specifically from var. 3, we should have to rely solely on the calcification or union of the scuta and terga; but we have seen this is a point which is variable in [Elminius Kingii], [Pyrgoma milleporæ], and in some species of [Balanus]. The serial affinities, moreover, in [Pyrgoma], clearly show that this is a character of no great importance. I must add that in several specimens of several of the varieties, the scuta and terga were so closely joined, that until careful examination, I was unable to detect the suture separating them; such being the case it must be quite unimportant for any functional purpose, whether or not the valves are calcified together. I feel, consequently, hardly any doubt that I have acted right in treating the present form as a mere variety.
Var. (10) an. spec.? fig. [6 t].—Hab. Unknown.—This variety bears nearly the same relation to var. 6, as the last variety did to var. 3. The shell is rather stronger than in var. 6, with the internal ribs not so prominent; and except in being tinted pale dull purple, it differs in no respect from the shell of var. 1. If we imagine the scutum and tergum in the third sub-variety of var. 6 ([6 p], [6 q]), in which the adductor ridge descends far beneath the true basal margin of the valve, to be calcified together, without any suture, we shall produce almost the identical valves of the present variety. The scutum, however, here is not quite so much elongated transversely, and the occludent margin is spinose and is furnished with large teeth; these two characters give the valve a somewhat different aspect, and hence I am more doubtful than in the foregoing case, whether this form may not be specifically distinct. I must, however, state that in [Tetraclita porosa], I ascertained that the teeth on the occludent margin of the scuta were even more variable than here is supposed to be the case; and as for the shape of the valve we have seen what wonderful variation there is in var. 6. The tergum in this variety is about intermediate between the two common forms, in the sub-varieties of var. 6. As for the calcification of the two valves together, we have seen, under the last variety, how little important a character it is.
Var. (11) fig. [6 U], [6 u] [Creusia grandis, of Chenu, Tab. 1, fig. 2, but not fig. 2 a and b].—Hab. Singapore, associated with [Pyrgoma monticulariæ].—This variety is very closely related to the last. The shell, however, has a very peculiar aspect, which made me for some time think it must be specifically distinct. It is of a much brighter pink than in any of the foregoing varieties; the surface is marked with very prominent, distant ribs, and the radii are narrow, in which latter points, together with the tint (though here brighter), this variety cannot be distinguished from var. 7. The shell, however, is permeated by several rows of pores, in which respect it resembles the shell in var. 2, and some specimens of vars. 3 and 4. In the opercular valves there is a close general resemblance with those of the last var. 10; the tooth, however, near the rostral angle, is not so prominent; and in the tergum, the spur is more truncated, shorter and broader than in var. 10, and closely resembles that in var. 1 and 2. But I cannot consider any of the points here specified of much weight.
The foregoing descriptions show how singularly the affinities of the several varieties interlock in the most complicated manner. Hereafter some one may, perhaps, succeed in grouping several of these forms as species; but I am sure he ought not to attempt it without possessing a very large suite of specimens, or without the great advantage of comparing some two or three of the forms, fresh in their native site.
Species dubiæ.—Under [Pyrgoma], I have stated that though Chenu, in his ‘Illust. Conch.,’ has given beautiful external figures of the shells, imbedded in the coral, yet from the want of details on the opercular valves and on the structure of the shell, I cannot recognise his species. So it, likewise, is with [Creusia]. Chenu gives the following new species; C. radiata, multistriata, decorata, and striata. The C. madreporarum, I suspect to be the [Pyrgoma milleporæ] of this work, as there stated. The C. grandis no doubt is the [P. grande] of this work, the Nobia grandis of Sowerby. The name Creusia Childreni is given by Dr. Gray, without description or figure, in the ‘Annals of Philosophy,’ vol. 10, new series, 1825.
7. Genus—CHELONOBIA. Pl. [14]: Pl. [15], fig. [1].
CHELONOBIA. Leach. Journal de Physique, tom. 85, (1817).
CORONULA. Lamarck. Animaux sans Vertèbres, 1818.
-------- Ranzani. Memoire di Storia Naturale, 1820.