POROMYA. 45 



The structure of the shell is very remarkable, although 

 not differing much from that of Thracia. The external 

 layer consists of crowded oblong cells having their ends 

 outward, and the inner layer is nacreous ; the cellular 

 part is easily rubbed off. The mantle is said to be open 

 in front, an unusual character in this group. Further 

 particulars of the animal are desirable. 



This genus is the Embla of Loven, and (according to 

 Chenu) the Eucharis of Recluz. 



tff 147 POROMYA GRANULA'TA*, Nyst and Westendorp. K 



Corbula granulata, Nyst & West. Coq. Foss. d'Anvers, p. 6, pi. 3. f. 3. P. 

 granulata, F. & H. i. p. 204, pi. ix. f. 4-6, and (animal) pi. W. f. 2. 



BODY creamcolotir : mantle open in front : tubes encircled at 

 their bases by a fringe of 18 or 20 tentacular filaments, which 

 expand like the petals of a flower, and are sometimes folded 

 back on the posterior side of the shell : foot very transparent. 



SHELL somewhat quadrangular or rhomboidal (the right 

 valve larger than the left and slightly overlapping it), mode- 

 rately convex, fragile ; externally it is opaque and of a dark 

 hue, but when the superficial or granular coating is removed, 

 it is semitransparent and glossy : sculpture, very minute and 

 close-set tubercles of nearly equal size, arranged in longitu- 

 dinal rows, and occasional but slight marks of growth : colour 

 dusky outside, and whitish under the surface-layer : epidermis 

 dark brown, visible only at the edges, and especially at the 

 back (where it forms a kind of elongated ligament on both 

 sides of the beak) : margins, rounded on the anterior side, 

 slightly curved in front, indented near the posterior side, which 

 is obliquely truncated and has a distinct ridge extending from 

 the beak to the posterior angle, with a broad fold on either 

 side of it ; posterior dorsal margin longer and straighter than 

 the other : beaks blunt and calyciform ; umbones prominent : 

 cartilage yellowish -brown, set rather obliquely in an obtusely 

 angular receptacle, which does not project far within : hinge- 

 line gradually curved : hinge-plate thickened on both sides of 

 the beak : teeth, in the right valve an erect, blunt and tuber- 



* Granulated. 



