CORBULIDZ. 139 
BOTHROCORBULA, Gabb, 1872. Differs from the typical Corbule 
in having a deep lunular pit under the beaks, penetrating and 
almost passing through the hinge-plate. C. viminea, Guppy 
(evil, 36, 37). 
PTEROMYA, Moore. Resembles Corbula, but thin; smooth or 
concentrically striated. Pt. Crowcombei, Moore. Rheetic beds, 
at Beer-Crowcombe. 
HIMELLA, H. Adams, 1860. Shell thin, with the left valve 
larger than the right one, not gaping; hinge of the right valve 
with an indistinct tooth fitting into a pit in the left valve; 
cartilage internal, lying in both valves in an almost horizontally 
extending process; an external ligament is besides present ; 
pallial sinus scarcely noticeable. Based on H. fluviatilis, Mara- 
non Riv. 
poramomyA, J. Sowerby, 1834. (Azara, d’Orbigny, 1839.) P. 
gregaria. Hocene; Isle of Wight. Cartilage-process broad and 
spatulate, received between two obscure teeth in the right valve. 
The estuary Corbule differ very little from the marine species. 
C. labiata lives buried in the mud of the River Plata, but not 
above Buenos Ayres, and consequently in water which is very 
little influenced by the superficial ebb of the river. The same 
species is found in banks widely dispersed over the Pampas near 
San Pedro, and many places in the Argentine Republic, five 
yards above the River Parana. (Darwin.) CC. erodina, Lam. 
(evi, 23-25). 
CORBULAMELLA, Meek and Worthen, 1857. Shell subtriangular, 
subglobose, inequivalve, the right valve being more ventricose 
than the left; beaks nearly central; hinge with one cardinal 
tooth in each valve, apparently very similarly arranged in position 
to that of Corbula, but the existence of an internal cartilage has 
not as yet been satisfactorily proved; anterior muscular impres- 
sion rather indistinct, posterior on a special raised or projecting 
plate; pallial impression scarcely sinuated posteriorly. C. gre- 
garia, M. and H. (ev, 95). Cretaceous; Nebraska. 
PLEctTopon, Carpenter, 1865. 
Distr.—P. scaber, Carp. Catalina Isl., Cal. 
Shell thin, rough, rostrate ; dorsal margin twisted within under 
the umbones, forming the cardinal tooth; lateral teeth long, 
laminated ; cartilage-pit minute, concealed under the umbones ; 
posterior lateral tooth contiguous; pallial sinus small. 
Has the aspect of Theora, and appears allied to Nera. It is 
probable that the cartilage was strengthened by an ossicle. The 
great peculiarity is the twisting-in of the dorsal margin, which 
ascends the umbo in a very loose spiral. 
SpHENIA, Turton, 1822. 
Distr.—4 sp. Britain, W. Coast of N. Am., Red Sea. Bur- 
