and Shells of Massachusetts Bay. 63 
and slightly inclined to the summits ; color of the interior 
dull yellowish-white ; muscular impression well defined, 
bi-partite, the anterior one rounded or oval, posterior sub- 
triangular ; epidermis thin, smooth, dark olive with paler 
zones interposed between the incremental lines. 
Osservations. This shell, taken from the stomachs of 
cod in various parts of our bay, has, at first glance, some 
likeness to N. limátula, Say ; beton inspection, it differs 
from that, in being much less rostrated, and the posterior 
side being the longer ; the epidermis is also much darker, 
and the dingy white of the interior very different from 
the pure briliant white of Say's species. All the spe- 
cimens of that, which have fallen under my notice, have a 
pale radiation extending from the summit toward either 
extremity, which is never found upon this shell. 
In size and general aspect it is not dissimilar to N. 
Nicobaricus, Lk., an inhabitant of the Indian Ocean, 
differing from it principally in the position of the um- 
bones. 
It approaches, however, nearest to the fossil species 
found in Maryland and described by Mr. Say, under the 
name of N. levis, in his American Conchology, and 
figured plate xri. of the same work. I have never seen 
the shell itself, but judging only, from the description 
and figure, think it possible the myalis may be the living 
analogue of the levis. 
I have named it N. myális, from the similarity of its 
configuration to that of the young of Mya arenaria, Lk., 
for which, when deprived of its olivaceous epidermis, 
it might easily be mistaken. It does not appear to be a 
very uncommon shell, and it is a little surprising that it 
should have remained unknown to us so long. 
