394 MOLLUSCA. 
OrpeER ACE PHALA. 
Puotas PaTuLa (Gould). 
T. oblonga, papyracea, alba, inequilateralis, concentrice undato-striata, 
constrictione mediano partita ; latere antico triangulart, radiatim cos- 
tato, costis ad undas tuberculiferis ; latere postico subquadrato, in- 
ermt: margine cardinal revoluto, umbonem tegente sed non adnato, 
callum dentiformem instructo: cochlea subulata, arcuata: cavositate 
ad undas, costas et tuberculos indentata. 
Pholas patula, Goutp; Proceed. Boston Soc. Nat. Hist., u. 214. 
May 1850. Expedition Shells, 73. 
SHELL transversely oblong, very thin, white, inequilateral, concen- 
trically undate-striate, divided into two portions by a vertical constric- 
tion; anterior portion triangular, radiately ribbed, the ribs knobbed 
where the concentric waves cross them ; posterior portion subquadrate, 
simple; hinge margin revolute, spreading over the beaks, but not ad- 
herent to them, and presenting a tooth-like callus ; internal apophysis 
curved, subulate ; the interior is everywhere indented in answer to the 
ribs, waves and tubercles. 
Length three inches; breadth an inch and four-fifths ; height the 
same. 
Probably from the [astern Seas. 
This species is remarkable for the width of its valves. It nearly 
approaches P. latissima, Sowerby, and possibly may be the same 
species. It also resembles in form and sculpture P. truncata. 
Figures 497, 497 a, 497 b, three views of the shell. 
Mya pracisa (Gould). 
T. M. truncate similis, calcarea, epidermide corneo induta, ovata, anticé 
rotundata et ventricosa, posticeé angustata, compressa et truncata ; 
cardo dente trapezoideo, latiore quam elevato, postice declivo instruc- 
