196 
have induced many^ and myself amongst the number, to consider 
this shell as the young of gihhosm, Barnes ; but a very slight ex- 
amination serves to show that it is very distinct. The young of 
that species is always much more elongated transversely, not so 
thick, with the beaks much undulated, and the series of small 
cicatrices in the cavity of the beaks is parallel to the hinge mar- 
gin. As respects magnitude it approaches parvus, Barnes, which, 
however, has the beaks undulated, is rather thin, with oblique, 
small, cardinal teeth. Plate 41. 
Unio CAMPTODON. — Specific character. Beaks distinct from 
the posterior margin ; lamelliform teeth arquated at tip. 
Desc. Shell moderately thin, transversely oblong-oval, a little 
compressed, dark brownish, or blackish ) beaks with regular small 
undulations, behind the middle but remote from the posterior edge, 
but little prominent; ligament slope somewhat compressed, with 
two distinct compressed lines ; umbonial slope not elevated above 
the level of the disk ; anterior margin a little prominent towards 
the base and rounded ; lunule large ; posterior margin prominent, 
extending far behind the beaks and rounded ; base a little con- 
tracted in the middle ; within milk white ; teeth, a single rather 
long, oblique, undivided primary tooth in each valve ; lateral teeth 
rather slender, towards the tip a little arquated. 
Ohs. This interesting, new shell was sent to me by Mr. Bara- 
bino, who discovered it opposite to New Orleans in ponds. An 
exterior view of the shell would not immediately distinguish it 
from Alasmodonta edentula, nob., but the inner surface is quite 
different, and the armature of teeth separates them generically. 
PL 42. 
Unio LuouBPas. — Desc. Shell transversely subovate, inflated, 
dark brownish, wrinkled ; umbones prominent ; beaks not very 
prominent, eroded ; ligament margin slightly arquated ; ligament 
more or less concealed ; anterior margin very widely rounded, 
sometimes truncate or even subemarginate ; posterior margin rather 
prominent, but very short ; base often a little contracted in the 
middle ; within pale lilac ; cardinal teeth oblique, compressed, 
denticulated ; lamelliform teeth slightly arquated, granulated and 
striated at tip ; posterior accessory cicatrix rounded, rather deep ; 
anterior margin somewhat iridescent. 
