62 ANATOMY OF AM ASTRIDE. 



similarity has no doubt influenced the prevalent classification 

 to an undue extent. 



The distinction of Amastrida of the subfamily Leptacha- 

 tinince from the Ferussacidce is a difficult matter so far as the 

 shells are concerned. The pallial organs, teeth and male re- 

 productive organs are also similar; but the peculiar develop- 

 ment of the prostate gland in Amastridce is a perfectly tan- 

 gible and important differential character, which I over- 

 looked when discussing the question in Vol. XIX, p. 212. 



Several genera of Ferussacidce reach back to the Eocene, in 

 species not materially differing from the recent forms; so 

 that they must have been differentiated during Mesozoic time. 

 It is obvious that in such groups as Cochlicopa and Lepta- 

 chatina we have to do with very old stocks, which have 

 changed with extreme slowness. It is a fair inference that 

 the shell of Leptachatina is not greatly changed from the an- 

 cestral mesozoic or earlier stock which gave rise to the 

 Ferussacidce, Amastridce, Achatinellidce, Enidce, etc. 



Soft Anatomy of Amastridce. 



The animal is externally similar to Achatinella except that 

 the genital orifice is further back, near the mantle (Amastra, 

 Carelia, Laminella) . The pallial organs are also substantially 

 the same, except that the kidney is dilated laterally at the 

 base, and therefore triangular in the lower part. (Carelia 

 turricula, pi. 20, fig. 5,.) The kidneys of several species of 

 Amastra and Laminella do not differ materially. 



The jaw is strong, arcuate, and usually irregularly "stri- 

 ated" vertically. In Leptachatina (pi. 21, fig. 10, L. labiata) 

 it appears that the striation is caused by superficial overlap- 

 ping edges of very narrow vertical plates, which are firmly 

 united, as in the Bulimulidce. In Amastra and Carelia turri- 

 cula the jaw is very opaque and appears nearly or quite 

 smooth. Carelia ~bicolor is figured and described by Mr. Bin- 

 ney as with "ten stout ribs, denticulating either margin. " 

 Similar variation from smooth to ribless occurs in several 

 genera of Helicidce. The jaw of Laminella is like that of 

 Amastra. The radula is oblong, teeth not very numerous, in 



