203 
authors, I conceive leads to error, and ought to be condemned 
by every modern naturalist. Plate 49, fig. 2. 
Cerithium eerrugineum. — Specific character. Pale ferru- 
ginous, granulated by longitudinal ribs and transverse striae. 
Desc. Shell oblong-conical with longitudinal ribs rendered 
nodulous or moniliform by the passing of elevated spiral striae over 
them; ribs about twenty on the body whorl, almost interrupted 
by the interstices of the striae ; striae about seven, with inter- 
mediate smaller ones on the body whorl, and but three on the 
second whorl; volutions seven; suture inconspicuous; aperture 
oblique, oval, whitish within ; labrum slightly thickened on the 
exterior margin, and with obsolete impressed lines on the inner 
side corresponding with the exterior striae ; color ferruginous. 
Ohs. Communicated by Mr. Elliott as an inhabitant of the 
southern coast of Plorida. Its general form is similar to that of 
the preceding species, but it is smaller, its elevations are more 
rounded like granules, and its ribs are not bifid. Plate 49, fig. 3. 
Mytillus. — Shell equi valve, inequilateral, obliquely elongated, 
more or less ovate-acute or subtriangular, or subcuneiform, regular ; 
summits posterior and terminal, acute ; anterior extremity obtusely 
rounded ; posterior base a little gaping to permit the passage of 
the byssus ; ligament marginal, deeply seated, subinterior, recti- 
linear, elongated ; hinge edentulous, or with one or two rudiments 
of teeth ; two principal remote muscular impressions, of which the 
anterior one is large and elongated ; palleal impression entire. 
Ohs. This genus has been considerably modified since it came 
from the bands of our great master Linne, who united in one as- 
semblage shells of divers characters, and constructed by animals 
of opposite habits, forms and organization. Brugui4re distinguished 
the widely different genera Anodonta and Avicula ; Lamarck 
separated Modiola, and Leach parted from Avicida the celebrated 
pearl shell of Celon under the name of Margarita, which was 
afterwards called Meleagrina by Lamarck. Cuvier instituted the 
genus Lithodomus, for M. lithodomus, and some other species 
which perforate and reside within calcareous rocks. But of these 
the most closely allied to the present group are unquestionably 
Modiola and Lithodomus, which two are united together by La- 
marck, and are considered by Blainville only as subgenera of My- 
