P H L A S. 



Species 12. (Mus. ?) 



Pholas Darwinil Pho. testd parvd, fused, hrevi, 

 antice latissiine apertd, radiatim scabrd, in medio 

 per sidcum foveolatum divisd, post sidcum concen- 

 trice nigatd, margine late recurvo ; valvuld dorscdi 

 nulld. 



Darwin's Pholas. Shell small, brown, short, an- 

 teriorly very widely gajiiug, radiately scabrous, 

 divided in the centre by a pitted sulcus ; behind 

 the sulcus concentrically ridged, with the margin 

 widely recurved ; no dorsal valve. 



SowERBT. Proc. Zool. Soc, 1849. 



Hah. Chiloe. Ch. Darwin. 



A curious little species, which might be likened to 



the young of Pholas papyracca, with the margins 



broadly reflected and recurved. 



those of Pholas Chilomsis, but the form of the shell re- 

 sembles more nearly that of Pholas Candida. 



Species 13. (Fig. a, b. Mus. Brit.) 



Pholas laqiteata. Pho. testd tenui, sub/usiformi, antice 

 apertd, angustd, acuminata, spiniferd, medio ven- 

 iricosd, medio posticeque costellis vix elevatis et 

 rugis concentricis laqueatis decussatd ; postice sub- 

 attenuatd, acuminatd ; valvulis dorsalibus duabus, 

 super umbones locatis, nucleis anticis sub-approxi- 

 matis. 



The fluted Pholas. Shell thin, rather fusiform, an- 

 teriorly open, narrow, acuminated, spinous, cen- 

 trally ventricose, centrally and posteriorly decus- 

 sated with scarcely elevated ribs and concentric 

 ridges; posteriorly rather attenuated, acuminated; 

 dorsal valves two, placed upon the umboes, with 

 anterior, nearly approximate nuclei. 



SowERBY. Proc. Zool. Soc, 18-49. 



Hab. Isle of Plata. H. Cuming. 



The pair of plates covering the umboes resemble 



Species 14. (Mus. Brit.) 



Pholas truncata. Pho. testd latd, brevi, antice acu- 

 minatd, subrostratd, late apertd, radiatim acuti 

 costatd, margine dorsali refiexo, postice oblongd, 

 quadratd, truncatd, concentrice liratd; valvuld 

 dorsali unicd, nucleo postice fere terminali. 



The truncated Pholas. Shell wide, short, anteriorly 

 acuminated, subrostrated, widely open, radiately 

 acutely ribbed, dorsal margin reflected ; pos- 

 teriorly oblong, square, truncated, concentrically 

 ridged, dorsal valve single, with the nucleus 

 nearly terminal posteriorly. 



.Say. American Journ. of Sci., vol. ii. p. 321. 



Ilab. North America. 



Species 15. (Fig. a, b, c, Mus. Cum. in Brit.) 

 Pholas crucifera. Pho. testd subcylindraced, antice 

 obtusd, hand late apertd ; omnino costis a'ebernmis 

 imbricatis radiatd ; margine dorsali in forma 

 crucis reflexo, lamind corned tecto. 

 The cross-bearing Pholas. Shell subcylindrical, an- 

 teriorly obtuse, not widely open ; everywhere 

 rayed with very close imbricated ribs ; dorsal 

 margin reflected in the form of a cross, covered 

 by a horny plate. 

 SowERBY. Proc. Zool. Soc, 1834. 



Hab. Island of Puma in the Gulf of Guayaquil; found 

 in soft sandstone at half-tide. Also in the Bay 

 of Carraccas, West Columbia, in soft stone at low 

 water, and in hard clay, 13 fathoms deep, in the Gulf 

 of Nocoyo, Central America. 



A most remarkable species on account of the cruci- 

 form reflexion of its dorsal margin. 



March, 1872. 



