. from the Coast of Africa. 29] 
over the umbones, as broad as the shell, into which the mar- 
ginal plates intrude posteriorly, nearly to its centre. "These 
latter are slender and lanceolate, and may perhaps be more 
properly considered as one, so closely are they united. "There 
are also two firmly united lanceolate plates along the basal 
margins. The apophysis is slender, compressed, falcate. 
The shell is entirely closed, except a small, vertically com- 
pressed, posterior opening, which was probably enclosed by a 
tubular appendix. Indeed the proper valves seem to terminate 
acutely, at a little distance within the present opening, which 
seems to be constructed by an accretion much like that 
formed on Lithodomi. 
This Pholas belongs to the same group as P. Californica, 
Conrad, (P. Janellii, Desh.) and with others, which are in 
like manner closed anteriorly, and have supplementary ventral 
valves, have been separated as a subgenus from the gaping 
species under the name. " Pholadidea. 
PsawwoBrA riGLiNA. Pl. XXIV. Fig. 9. 
Testà erassá, sub-ovali, esr cipi rufo-cinered ; anticé rotundatà ; 
Posticé hiante, Sub-rostratà, valdé flexuosa, apice emarginatà: valvis con- 
centricé laminoso-striatis, radiatim ticdu: natibus elevatis, attigentibus ; 
dentibus cardinalibus divaricatis : intus alba, punctis numerosis i indentata. 
Long. 31; alt. 92; lat. 12 poll. ” 
Shell thick, nearly equilateral, suboval, acutely rounded 
before, posteriorly gaping, somewhat rostrate, very strongly 
Waved or folded, and emarginate at apex. Color a reddish- 
asn, Surface marked with close and somewhat E P 
aint 
other; margin behind the beaks straight and excavated. 
Hinge teeth divaricate, two in the right and one in the left 
ve. Within white, indented with numerous large punc- 
tures. Siphona] scar linguiform, narrowed at base, extending 
half the length of the shell. 
