NAVICELLA. 



bctvv eeii ii; and Crepidiila; and we tliink no otlier Genus 

 will be confomided with it. 



Shell transversely elliptical or oblongs regular^ convex 

 on the outside^, but concave within; without a spire^ vertex 

 turned downwards to the margin rather obliquely. In- 

 ternal lip narrow^ flattened^, sharp edged^ without teeth; 

 outer lip entire, sharp edg*ed, extending in young shells 

 beyond the point of the vertex, which in older specimens 

 is commonly eroded. If the shell be held in the position 

 which we have given it in our plate, and which most 

 clearly proves its affinity to Neritina, two elongated mus- 

 cular impressions Avill be distinctly observed, both of which 

 are transverse and one placed in the upper, the other in 

 the lower part of the inside; and the sharp edged inner 

 lip will become longitudinal. In mentioning the oper- 

 culum, we feel obliged to notice the opinion entertained 

 by some that it is an internal shelly piece of the animal, at 

 the same time we coincide entirely with Lamarck in opi- 

 nion, that its similarity in structure proves its analogy 

 with the shelly opercula of Neritina, Nerita, &c. it is of a 

 squarish form and shelly substance, thin, flat, and fur- 

 nished with a sharp point proceeding from the side at one 

 corner. 



The recent species of this Genus, few in number; are 

 natives of rivers in warm climates, they are brought from 

 India, the Isle of France and the Molucca's: they are na- 

 turally covered on the outside with a greenish brown and 

 strong epidermis, beneath which they are marked all over 

 with very dark coloured zigzag lines and triangular spots, 

 so that when the epidermis is taken ofl', it has the appear- 

 ance of a black shell with triangular whitish spots. We 

 are not aware of the existence of any fossil species, unless 

 indeed, a little shell, which we have added a representa- 

 tion of to our plate, and which De France calls Crepidula 

 altavillensis,* belong to this Genus. f 



We have not hesitated about adopting Lamarck's ge- 

 neric name, for though it was not first published by La- 

 marck, yet De Montfort was aware of Lamark's having 

 applied the term Navicella to these shells before he pub- 

 lished it under that of Cimbei'. 



* Diet, des Sciences Nat. torn XI. p. 397. 



f The cxuiniriHtion of several more specimens than we at first possessed, 

 have convinced us that this belongs to Neritina. 



