52 Lamarck's Genera of Shells. 



character of this family, (not noticed by Linneus,) consists in the 

 singular developement of the right lip of the shell at a certain age 

 of the animal, and especially, in a particular sinus which is con- 

 stantly found near the base of that lip when it has acquired its full 

 expansion. The operculum is horny, elongated and straight. 



Lamarck divides this family, which contains the true strombi of 

 Linneus, into three genera, founded on characters derived from the 

 canal at the base, and from those of the right lip of the aperture. 



1. Rostellaria*. 



Shell fusiform, or subturrited, terminated at the lower part by 

 a pointed, beak-shaped canal. Right lip entire, or toothed, more 

 or less dilated by age, and having a sinus contiguous to the 

 canal. 



The right lip of these shells rests, at the upper part, against the 

 elongated spire, and sometimes runs along it; but what especially 

 characterizes this genus is that the sinus at the lower part of the 

 same lip is quite contiguous to the canal, which is not the case, 

 either with the pterocera or strombus. 



Type. Rostellaria cur virostr 1st. (Strombus fusus. Linn.) 



Shell fusiform-turrited, very thick, heavy, smooth, very deli- 

 cately striated transversely, reddish brown ; whorls rather convex, 

 the last obsoletely plicate ; aperture white ; edge of the lip toothed ; 

 beak rather short, curved. Molucca Seas. PI. v. Fig. 184. 3 Re- 

 cent species, aud 3 fossil. 



2. PteroceraJ. 



Shell oblong oval, ventricose, terminated, at the lower part, by 

 an elongated canal. Right lip dilated by age, into a digitated 

 wing, the upper part of which rests against the whole spire ; a 

 sinus near its base. Spire short. 



The canal at the base of the shells of this genus, is not shortened 

 and truncated, as in the strombi, but elongated and caudiform, at- 

 tenuated towards the extremity, and frequently closed. The sinus 



* From Rostellum, a little biak. 

 * Curved beak. { From wlsjovj a wing, and xi^a?, a horn. 



