174 
i 
teeth denoted by an impressed line; cavity of tbe umbo sligbt. 
but with a deep, obvious and large muscular impression immedi- 
ately under tbe beak ; more or less tinged with purple, 
Obs. Tbe anterior emarginations, above mentioned, are obvious 
in many species, but are more particularly remarkable in tbe 
present shell ; they mark tbe situations of tbe tubes of tbe animal. 
Tbe form and arrangement of tbe teeth are very much like 
those of tbe monodonta, .nob., but tbe outline and other cbaracteus 
of this shell, as expressed in tbe above description and exhibited 
in tbe plate, are widely different. 
It is certainly an inosculating species between Unio and Ano- 
donta, but traces of tbe primary and lamelliform teeth are, I be- 
lieve, always discoverable. It is an inhabitant of tbe Wabash 
river, and is not uncommon. 
Tbe largest individual that has occurred, is in length one inch 
and three-tenths, and in breadth three inches and two-fifths ; but 
the plate exhibits the usual magnitude. The cavity of the beaks 
is often more or less tinted with purple. PL 24. 
SiGARETUS. — Shell ear shaped, univalve, spiral, depressed ; 
aperture very large, entire, embracing a portion of the preceding 
volution, much wider than long ; destitute of nacre : columella 
short, spiral : labrum simple : volutions two or three : muscular 
impressions two, distant : operculum none : a revolving slightly 
elevated line on tbe inner surface ; spire lateral : periostraca none, 
Ohs. These are marine shells, inhabiting various parts of the 
globe. Like Ovida, Oliva, &c,, the shell is included within the 
mantle of tbe animal. Of the few species yet discovered, Linne 
considered one a Helix. Lamarck adopted the name of the genus 
from Adanson, and placed it in his family of Macrostomes, with 
Stomatella, Stomatia and Haliotis, distinguishing it from the 
others by being destitute of. nacre. He says, it seems to have 
some relation to Natica ; and indeed some similarity is exhibited 
by the S. concavus of that author, and an allied fossil species 
which Mr. Hoeninghaus sent me under the name of canaliculatus. 
But as those shells are external, or not enveloped in the mantle 
of the animal, the relation must be considered as of analogy rather 
than of affinity. 
Cuvier, who examined the structure of the animal of a species 
of this genus, but we are not informed which, either by name or 
