REPTI I.I AN AGE. JUR A S S I C PERIO D. 105 



CLASS GASTEROPODA. 



SUBCLASS PfI..M()NIFi:i: \ 



ORDER Inopcrculatn. 



SUBORDER LIMXOP1UI. A 



FAMILY LIMN^EIDJS. 



Shell dextral or sinistral, thin, and born-colored, varying from elongate- 

 subeylindrieal to ovate or diseoidal; capable of receiving the entire ani- 

 mal when ivtrartnl : aperture simple; columclla with or without a fold; 

 lip sharp. 



Animal with a short dilated muzzle; tentacles short and compressed, 

 or elongate and slender, bearing the sessile eyes at their inner bases. 

 Mantle with its margin simple or very rarely digitate. Mouth armed with a 

 corneous upper mandible; lingual teeth numerous, arranged in transverse 

 rows, the central minute and the lateral uncinate. Respiratory orifice 

 ou the right side, and the vent at the left of the neck. Foot ovate or 

 lanceolate. 



The above diagnosis is framed so as to include three subordinate groups, present- 

 ing in their various species a wide range of forms, and more or less important 

 differences in the characters of the animal. These sections or subfamilies may be 

 characterized as follows: 



Shell spiral, dextral. Animal with tentacles short and flattened, or triangular. 

 Includes Limaaa, and probably CAi/ina aud Amphipeplea. 



2. Phyainae. 



Shell sinistral, otherwise mnch as in the Limnainte. Animal with tentacles elongate and slender. 

 Includes 1'hysa, Phytoptu, Aplexa, Afacropkyta, 1 and Camptocertu. 



3. Planorbiuac. 



Shell involute, discoidal, dextral, or sinistral' f aperture more or less crescentio. Animal with tentacle* 



as in the PHyiinee. 

 Includes Plaaorbu Tapkiut, Bathyompkaltu, Gyraulut, and Stymentina. 



Notwithstanding the striking differences of form observed in the shells here 

 ranged under the sections of this family, the animals of these several types agree 

 in so many respects, that conchologists generally place them together in one family; 

 while some also include Aneylus, Acroloxus, Latia, and GrundlacJiia. 



1 Macrophysa, Meek. The type for which this name is proposed is the curious Eocene species 

 described by Deshayes (Coq. FOBS. II, 90; X, 11 and 12) under the name Phyxa columnaris. It 

 is a remarkably elongated, subcylindrical shell, with a deep suture, and a comparatively very email 

 body whorl. Its aperture is oval and small, or less than one-third the entire length of the shell, 

 angular behind, and subangular or abruptly rounded in front ; columella smooth, flattened, and some* 

 what twisted. It seems to be intermediate between Camptoceras and Aplexa, and may possibly be 

 ranged as a subgenus under the latter. 



See note, p. 106. 



14 December, 1864- 





