AWE'S WX. 
0 
ARCOPERXA. Conrad. 
A. Carol Inensis , pi. 1, fig. 0. Shell snboval, inflated, beak prominent 
terminal, lunge and ventral margins parallel; posterior end rounded. 
IXOPEGNA. Conrad. 
Shell profoundly elongated, of a mytiloid form ; hinge entire? concen- 
trically plaited on one side and longitudinally striated on the other or basal 
half of the valves; hinge and ventral margins subparallel; posterior end 
rounded. 
This is an extremely thin shell, very pearly, and having undulated ribs 
or plaits very like those of many species of Inoceramls. I have had 
only a partial view of the hinge, and therefore cannot state its character 
with certainty. The substance of the shell is fibrous like that of Inocer- 
amus to which it is nearly allied. 
To this genus I refer Modiola yiieata, Sowerby ; M. fiagellifera, Forbes, 
and Inoceramus sill qua, Matheron. 
I. Carolinensis, pi. 1, fig. 22. Shell slightly arcuate towards the pos- 
terior end, much compressed, gradually expanding to the posterior 
extremity, which is rounded. 
The shorter outline and larger ribs distinguish this species from the 
allied forms. The compression of the valves may be owing to pressure, 
one valve being perfectly flat. 
MYTILUS. Lin. 
Al. condecoratus, pi. 1, fig. H). Shell small, ventrieose, slightly in- 
curved; disk undulato-plicate concentrically; substance pearly; beaks 
oblique, prominent, acute. 
I found only one valve of this beautiful shell. 
M. nasutus , pi. 1, fig. 9. Shell broadly triangular, suddenly depressed 
anteriorly, incurved, rostrated; beaks acute and very oblique. 
A r ery rare. One specimen has concentric plicae near the beaks. 
ETEA. Conrad. 
Shell equivalved ; right valve with one primary cardinal triangular bifid 
direct tooth under the apex and a pit on each side ; 2 lateral teeth, ante- 
rior, one approximate, robust; a broad cavity between it and the hinge 
