274 



LAND AND FRESH-WATER SHELLS OF N. A. [PART T. 



Fig. 490. 



Jaw with broad, crowded, anterior ribs and marginal deu- 

 ticulations. 



The lingual ribbon is broad, composed of a 

 median row of tricuspid denticles, the central 

 toothlet of each being long and acutely pointed, 

 the side toothlets short and blunt. The lateral 

 teeth are modifications of the central, 31 in number, 

 but bicuspid, the inside toothlet of the central being omitted in 



Jaw of 

 Arion fiiscu- 

 [JIoq.-Tand.] 



Ficr. 491. 



mmmmMmm 



Liugual dentitioa of Arion ftiscus. 



the laterals on the side nearest the central line, and the teeth 

 gradually changing as they pass off laterally. 



The genus Arion was separated from Limax by M. Ferussae, 

 to contain those species of the latter genus having a tei-minal 

 pore or sinus. It is universally recognized, and has been fortu- 

 nate in escaping any confusion of synonymy. 



The habits of the Xorth American species have been given 

 under Limacidse. 



The internal calcareous grains which represent the shell are in 

 some species isolated, in others aggregated into a nearer re- 

 semblance to the internal plate of Limax. On this distinction 

 are based the subgenera Lochea and ProJcpis. 



SuBGEN-rs PROLEPIS, Moq.-Tand. 



Shield covering an imperfect, rugose, shell-like plate, formed 

 by the aggregation of a certain number of calcareous granu- 

 lations. 



