GENUS CHELONOBIA. 383 



panded ends of the folds) and the internal surface of the shell, 

 but the open spaces between the folds are occupied by the 

 epidermis of the Whale, and are external to the cirripede. 

 In Chelonobia, the parieties are remarkably thick ; hence 

 the plates or septa, connecting the outer and inner lamina, 

 are of unusual length ; and the spaces between them, 

 though of course internal with regard to the cirripede and 

 occupied by the ovaria, have been compared to the spaces 

 external to and between the folded walls of Coronula. There 

 is but little special affinity between these genera ; and I 

 regret that they have come to be placed one after the other in 

 this work: but the elongated opercular valves, — the thick and 

 double opercular membrane, — the weak depressor muscles, 

 — and the peculiar manner in which the scutum is articu- 

 lated by the aid of a horny projection to the tergum, may 

 indicate some real but slight affinity to Coronula ; the many 

 points of difference, however, in the structure of the shell 

 and of the opercular valves, and especially in the cementing 

 apparatus of the basal membrane, and in the branchiae, all 

 prove that the genera are very distinct. The singular 

 structure of the rostrum, which, in fact, consists of three 

 compartments externally blended together, and which three 

 correspond in all essential respects to the rostrum and two 

 rostro-lateral compartments in the Chthamalinge, offers a 

 very striking point of identity with that sub-family; but 

 neither in the mouth, cirri, or other part, can I detect any 

 other evidence of this relationship. Having so far discussed 

 the affinities of the genus, I may acid, that the three species, 

 though decidedly distinct, are closely and nearly equally 

 related to each other. 



General Appearance. — The shell is generally depressed, 

 and broadly oval or almost circular; in C. testudinaria and 

 caretta, it has a massive appearance : the surface is gene- 

 rally smooth, or, when disintegrated, finely striated: the 

 colour is white. The six compartments do not differ much 

 in size : the rostrum is rather larger than the carina, and 

 the lateral compartments, than the carino-lateral compart- 

 ments. It is remarkable that in C. caretta (PI. 14, fig. 2), 

 even in specimens which have not grown crowded together, 

 the compartments are almost invariably placed rather un- 



