GENERA AND SPECIES. 



235. agrestis, animal ij in. 



236. lavis, 



237. tenellus, 



shield marked with concentric lines ; shell 

 small and oblique ; keel on back set 

 obliquely. 



animal dark brown, tinged with violet ; shell 

 square and minute, breathing hole near 

 centre of mantle's right margin. 



yellow mantle, body greenish white, head and 

 tentacles black, shell oval, shield wrinkled, 

 mucus yellow. 



greyish, spotted with yellowish white, 

 central darker stripe, and a darker band on 

 each side ; shell nearly flat. 



grey, spotted and striped with black, 

 tentacles long and purple ; shell oblong ; 

 ^ in. by - in. 



breathing hole marked with darker tint than 

 body ; sole with white band in the middle. 



Among the varieties of 234 are grisea and suffusa, both of which are grey, the former 

 having brown and white tessellations. 



Of 235 there are nearly a dozen varieties, nigra being jet black, Jilans being greyish- 

 white, punctata and nigricans being spotted with black, lilacina. being spotless, the usual 

 albida, and subtnaculata. which is streaked and spotted. 



Of 236 there is but one variety maculata which is spotted dark brown. 



Of 238 there are three varieties bettonii, which has white and ruddy spots ; dicipiens, 

 which has pale spots on a dark grey ground ; and maculata, which is spotted with black, 

 and has a thin band on each side. 



There are some nine varieties of 239, among them being cinerea, which is ashy with a 



238. arborum, 



239. maxtmus, 



240. ctnereo-mger, 



3 in. 



6 in. 



4 in. 



black mantle ; ferrussaci, which is white, with four rows of black spots ; cellaria, which is 

 ashy with black spots and bands ; fasciata, which is ashy white with five whitish bands ; 

 obscura, which is brown ; rufescens, which is ruddy ; and marmorata, which is marbled 

 with brown. Of cinereo-niger there is a black variety nigra. 



Llmnsea. (LtMtfMIDM.) Plate xvii. 



207. auricular ia, i J in. whorls 4 or 5, last whorl enlarged ; spire 



short and acute, inner lip forming small 

 umbilical fissure behind it. 



208. glabra, in. whorls 7 or 8, spire long, mouth with 



broad internal white rib. 



209. glutinosa, J in. spire very short but not sunken ; whorls 3 



or 4, last whorl forming nearly the whole 

 of the shell ; suture shallow, mouth oval 



210. involute, in. spire very short and sunken, suture deep, 



mouth pyriform. 



211. palustris, i in. whorls 6 or 7, less rapidly enlarging than 



213 ; spire long, suture deep. 



212. feregra, f in. whorls 5, last whorl enlarged, inner lip 



folded on pillar and forming narrow groove. 



213. stagnalis, 2 in. whorls 7 or 8, last whorl enlarged, suture 



deep. 



214. truncatula, f in. whorls 5 or 6, spire long, suture very 



deep, umbilical fissure distinct. 



There are over sixty varieties of the species of Limnaa, most of them differing from the 

 type in having a larger or smaller lip and a longer or shorter spire ; some are decollated, 

 some sinistral, some white, but as a rule the differences are so slight that it has hitherto been 

 impossible to describe them satisfactorily. 



