A M P U L L A R I A leucostorna, 

 White-mouthed Apple Snail. 



Generic Character. — See PI. 98. 



SpEcinc Character. 



A testa ovatd, rugosd, epidermide olkaceo-fuscd ; lahio exteriore 

 tenui ; aperturd albd ; mnhilico xix clauso. 



Shell oval, wrinkled ; epidermis olive-brown ; outer lip thin ; 

 aperture white ; umbilicus nearly closed. 



In prosecuting ray illustrations of this genus, I have care- 

 fully examined all the specimens in the cabinets of my 

 friends, and have added many to my own. These materials 

 have thrown some additional light on those species which 

 I have already described, and have enabled me to detect 

 several others altogether new. Among the latter is the 

 shell here figured, and which is so rare, that I know but 

 one example of it in this country. Its form is more 

 oval than that of A. rugosa, from which it is likewise 

 distinguished by a very small umbi'icus, nearly concealed 

 by the inner lip ; the wrinkles are numerous and unequal, 

 the spire pointed, and the aperture milk-white. 



Since my remarks on the Pianorbis cornu-arietis of 

 Lamarck were published, it has been discovered that the 

 shell is furnished with an operculum : one of these is in the 

 possession of Mr. Sov»'erby : thus what was a matter of 

 doubt becomes a fact, and affords the only substantial argu- 

 ment for terming it an Ampiillaria. On the other hand, 

 its affinities to Pianorbis (marked by its discoid, depressed 

 form, and the total absence of the pillar,) remain in no 

 degree impaired. The weight of argument on both sides 

 now appears to be so equal, that it is a matter of no 

 moment whether this shell be placed in the system at 

 the end of the Ampidiaricc, or at the commencement of 

 the Planorbcs. To the generality of conchologists, the 

 latter collocation would appear the most simple ; but, on 

 the whole, I incUne more to the propriety of considering 

 it the terminal species of the Jmpu/laricc, or that 

 which marks their transition (as I before observed) to the 

 Planorbes. 



PI. 175. 



