489 



13. Pholas crucifeua (pi. civ. f. 24, 25, 26), Sowcrby, 

 Pro. Zool. Soc, 1834, p. 69. 



Ph. testa utrinque obtusa, haud late aperta ; costis creberrimis, 

 imbricatis, omnino radiata; lamina dorsali cornea, ad umbones 

 super marginem reflexum in crucis forma posita. 



The dorsal margin of the shell is reflected over the umbones so 

 as make a cross-shaped platform for the reception of the accessory 

 valve, which is horny, and in maturity spreads over the dorsal 

 margins. The ribs are close, and closely imbricated. The ventral 

 opening is not large. 



Found in soft sandstone at half-tide on the shores of the island 

 of Puma, in the Gulf of Guayaquil ; in soft stone at low water in 

 the bay of Caraccas, West Colombia ; and in hard clay, in thirteen 

 fathoms water, in the Gulf of Nocoiyo, in Central America. 



14. Pholas crispata (pi. civ. f. 37), Linn. Syst. Nat. 1111. 



Ph. testa ventricosa brevi, in medio canali constricto divisa ; 

 antice angulari, late hiante, imbricis acutis radiatim ornata ; pos- 

 iice substriata, subrotundata. 



With the exception of Ph. latissima, this species is the broadest 

 of any in proportion to its width. It gapes very widely in front, 

 and is divided in the centre by a grove, the anterior portion being- 

 imbricated by strongly raised angular points in radiating series, 

 and the posterior part nearly smooth. There is no accessory 

 valve ; but the dorsal edge is strongly reflected over the umbones, 

 and the tubes of the mollusk are protected by an external epider- 

 midous case. 



Great Britain. 



15. Pholas constricta (pi. civ. f. 27, 28), Sowerby, junr., 

 Pro. Zool. Soc, 1849. 



Ph. testa ventricosa, antice utrinque aperta ; in medio area an- 

 gusta, constricta, oblique divisa ; antice radiatim scabrosa, postice 

 minute concentrice striata; ad marginem dorsalem postice reflexa. 



Resembling Ph. parva, but without any accessory valve, and 

 having a double dividing line across the centre, as in Ph. 

 papyracea, &c. 



Collected by Mr. Cuming at the Straits of Sunda. 



16. Pholas latissima (pi. ciii. f. 15, 16), Soiverby, junr., 

 Pro. Zool. Soc, 1849. 



Ph. testa subquadrata, subcompressa, aperta, antice angulata, 



