MONOGRAPH OF THE GENUS 

 ST 11 OMB US. 



Char. Gen. Molluscum marinum ; testa conica, spirali, ventri- 

 ■cosa, cras9a ; spira conica, plerumque plicata, acuta ; apertura. 

 plerumque angustata, postice canaliculata, antice in canalem 

 brevem emarginatum desinente ; labio interne- plerumque incras- 

 sato; labio externo aetate dilatato, postice plus minusve emargi- 

 nato, unilobato, medio intiis incrassato, antice sinu e canali dis- 

 tincto, interrupto ; operculo corneo, pyriformi, nucleo terminali. 



In conformity with the plan announced in the first page of this 

 number, the author contents himself with stating the characters 

 of this genus as generally understood, without presuming at 

 present to attempt such a definition as would prevent the possi- 

 bility of shells being confounded with it which do not belong to it; 

 it will, however, be perceived, on glancing over the plates, that 

 there is an indescribable peculiarity in form and appearance by 

 which most persons in the habit of seeing shells would know a 

 Strombus at first sight. The shells belonging to this genus are 

 spiral, conical and thick, with the spire conical, and generally 

 plicated near the apex, the aperture is narrow, with a canal close 

 to the body whorl, near to or upon the spire, and a short anterior 

 canal, sometimes produced into a truncated beak ; inner lip gene- 

 rally thickened with age ; outer lip, when full grown, dilated, at 

 the spiral extremity more or less elevated, emarginated, and having 

 a single lobe, in the centre thickened within, generally inflected, 

 and having a sinus near to the anterior termination, but distinct 

 from the canal ; operculum horny, pyriform, terminated by the 

 nucleus anteriorly in a point. The difference between Strombus 

 and Rostellaria is stated to be that in the latter there is no sinus 

 in the outer lip distinct from the canal. In Pteroceras, the ante- 

 rior canal is lengthened into a caudal appendage, and the outer lip 

 is digitated. Strombi are found in seas of warm climates. In 

 the following arrangement of species we commence with two be- 

 longing to a form which may probably hereafter be erected into a 

 genus, the character of the anterior and posterior canals presenting 

 a strong resemblance to those of Rostellaria, but having in the 

 species now described a distinct though shallow sinus in the outer 

 lip. There are, however, fossil species of the same general form 

 without the sinus. 



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