424 BALANID.E. 



9. Genus — Platylepas. PL 17, fig. 1 and 2. 



Platylepas. J. E. Gray. Amials of Philosophy, (new series), vol. x 



(1825). 

 Coronula. De Blainville. Diet, des Sciences Nat. (1S24). 

 Columellina. Bivona (fide Philippi). Nuovi generi, &c. di Mol- 



luschi, Palermo (1832). 



Compartments six, each bilobed and inioardly produced, 

 so as to form six midribs, ivhich support the outwardly 

 convex, me?nbranous basis. 



Distribution, throughout the tropical and warmer temperate seas. Imbedded 

 in turtles, sea-snakes and manatee. 



This small genus, consisting of three species (though I 

 have named only two), is a very natural one, yet closely 

 allied to Coronula. Most authors have united these genera, 

 but in doing so they destroy two very natural little groups. 

 Platylepas, moreover, when all its characters are considered, 

 has as good a claim to be generically separated from Coro- 

 nula, as has Tubicinella, — a genus universally admitted. I 

 shall presently recur to this subject. 



General Appearance. — The most remarkable character, 

 and which gives a peculiar aspect to the whole shell, is that 

 each of the six compartments has a medial fissure or fold ; 

 the shell thus consisting of twelve lobes. Each fold extends 

 from the summit to the base of the shell, and is produced 

 inwards in the shape of a midrib (PI. 17, fig. 1 a). The mem- 

 branous basis is supported by the basal edges of the six mid- 

 ribs, and is thus rendered convex. As the midrib on the 

 rostrum would have interfered, if fully developed, with that 

 part of the animal's thorax which I have called the prosoma, 

 it is of less size than the other midribs ; and from this same 

 cause the whole rostum is pushed a little on one side, gene- 

 rally to the left, so that the shell is not perfectly symmetrical. 

 The midrib of the carina is less than the lateral midribs. 

 The orifice is oval, and is more or less plainly indented by 

 six angular points, — the worn-down summits of the six mid- 

 ribs. The narrow elongated opercular valves stretch from 



