493 



striated, the posterior laminae of the epidermis are more minutely 

 serrated, and the external laniina3, covering the dorsal edge, are 

 very differently shaped, the posterior pair being trilobate. 



24. Pholas calva (pi. cv. f. 51, 52, 53), Sowerhy, Pro. 

 Zool. Soc, 1834. 



Ph. testa subpyriformi, clausa, antice ventricosa, in partes tres 

 oblique divisa ; ])arte antica prope marginem ventralem laevigata, 

 in medio et ad dorsum minute radiatim scabra ; parte media late 

 plana, epidermide crassa induta ; parte postica subrotundatim an- 

 gulata, attenuate, epidermide laminata, fascia serrata marginata ; 

 margine ventrali integumento elongato, iutegro ; margine dorsali 

 integumento subtestaceo super umbones et latera, marginibus 

 lobatis, expanso, postice altero elongato inter lobas integumenti 

 postici paululiim intruso. 



Differing from Vh. acuminata in the shape of the laminse and 

 termination of the posterior portion, which are rounded, and in 

 the external dorsal covering, or shield, which is more shelly, and 

 spread over a large portion of the sides of the shell as well as the 

 umbones, and the posterior dorsal integument is intruded a short 

 space between two of its lobes. 



Collected by Mr. Cuming in very hard stone at low water, in 

 Panama Bay. 



25. Pholas branchiata (pi. cviii. f. 82, 83), Gould, Pro. 

 Bost. Soc. Nat. Hist., 1845, p. 290. 



Ph. testa clausa, subpyriformi, ventricosa, in partes tres oblique 

 divisa ; parte antica prope marginem ventralem sublsevigata, dorso 

 usque ad medium minute striata ; parte media plana, epidermide 

 crassa induta ; parte postica ad terminum attenuata, epidermide 

 in laminis laevigatis rotundatis disposita; margine ventrali integu- 

 menti elongato, integro ; margine dorsah lamina testacea super 

 umbones, lateraliter et subantice expansa, marginibus integris; 

 postice integumento elongato claviformi, usque ad medium lamina? 

 umbonalis intruso. 



Differing from Th. calva in the shape of the umbonal plate, 

 which is less spread, and more even and entire ; and in that of the 

 posterior dorsal integument, which is intruded half-way into the 

 umbonal plate. 



26. Pholas ovata (pi. cvii. f. 71, 72), Gray, MS. British 

 Museum. 



Ph. testa subpyriformi, ventricosa, clausa, in medio transverse 



3s 



