203 



authors, I conceiA'e leads to error, and ought to be condemned 

 by every modern naturalist. Plate 49, fig. 2. 



Cerithium ferrugineum. — Specific character. Pale ferru- 

 ginous, granulated by longitudinal ribs and transverse strire. 



Desc. Shell oblong-conical with longitudinal ribs rendered 

 nodulous or moniliform by the passing of elevated spiral strijB over 

 them ; ribs about twenty on the body whorl, almost interrupted 

 by the interstices of the stria9 ; strire 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 Florida. 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 equivalve, 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 hands 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. Brugui^re 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 LitTiodomus, for 31. lithodormis, 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 LitJiodomusj which two are united together by La- 

 marck, and are considered by Blainville only as subgenera of My- 



