IX. SYSTEMATIC DISCUSSION OF SPECIES. 



Family LYMNiEID^E Broderip, 1839. 



Subfamily Lymn^ein^e Dall, 1870. 



Shell : Normally dextral, rarely sinistral, ovately-oblong or 

 elongate ; spire more or less attenuated ; columellar axis thickened by 

 a shelly deposit and typically gyrate or twisted; peristome thin, sharp; 

 shell covered with a corneous periostracum or epidermis. 



Animal: With a short, wide, rounded foot; head supporting a 

 velum which is retained from the larval state ; tentacles flattened, tri- 

 angular, the eyes sessile upon their inner base ; a large superior and 

 two smaller, narrow, lateral jaws present; central tooth unicuspid, 

 lateral teeth bi- or tri-cuspid, marginals serrated; kidney very large, 

 wide, pear-shaped ; ureter proceeding directly forward without flexure ; 

 buccal retractors two in number, very long, inserted distally in the 

 columellar muscle, the right retractor near the penis retractors and 

 the left retractor some distance from this point; genitalia with the 

 genital apertures separated, that of the male being behind the right 

 tentacle, while that of the female is at the base of the neck near the 

 pulmonary opening; the male organs consist of penis, penis-sac, vas 

 deferentia, and prostate ; the female organs consist of vagina, oviduct, 

 receptaculum seminis and one albuminiparous gland with two accessory 

 glands ; an ovotestis and ovisperm duct are common to both male and 

 female systems. The penis and penis-sac are retracted by one or more 

 powerful muscles which are inserted in the columellar muscle. The 

 body of the animal is striated, not granulose as in the helices. 



Distribution : Worldwide, but more numerous in the north tem- 

 perate zone. 



Geological Range: Upper Jura (Purbeck) to recent fauna. 

 Maximum development in late Tertiary times. In America the family 

 ranges as far back as the Comanchean Period. 



As restricted above, the Lymnasinse form a markedly uniform and 

 well-characterized group of the fresh-water Pulmonata. 



