6-i 



THE CHICAGO ACADEMY OF SCIENCES. 



Of the above regions, the Canadian has produced the largest 

 number of species (14). The Greenlandian region has but one peculiar 

 ies, and the West Indian. Carolinian and Alaskan regions have but 

 two species peculiar to their areas. 



A study of the distribution maps reveals certain interesting facts 

 regarding the present dispersal of Xorth American Lymnaeas. The 

 largest number of species is found between the 38th and the 60th 

 degrees of north latitude. Xorth and south of these parallels the 

 number of species notably decrease. 



TABLE SHOWING DISTRIBUTION' IK LATITUDE. 



Species and varieties north of 60° 13 



Species and varieties between 38 ° and 60" 85 



Species and varieties south of 38° 29 



Species and varieties south of 30 : 7 



Species and varieties south of 20° 3 



It will be noted in the above table that the number of species first 

 increases and then decreases, the number steadily falling until but three 

 species are represented south of 20°. This table also indicates the 

 northern distribution of the family. 85 species and varieties, or 85 per 

 cent being found between 38° and 60° of north latitude. It is note- 

 worthy that but three species of Lymnceas have been recorded from 

 the tropical zone. 



SPECIES AND VARIETIES NORTH OF 60°. 



stagnalis apprcssa. holbollii. vahlii arctica. 



stagnalis zcasatchensis. obrussa. randolphi. 



truncahila. palustris. alaskensis. 



perpolita. vahlii. petersi. 



vahlii pingelli. 



SPECIES AXD VARIETIES BETWEEN 38" AND 60°. 



stagnalis appressa. humilis rusiica. traskii. 



stagnalis peratnpla. ferruginea. vahlii. 



stagnalis lilliance. obrussa. vahlii arctica. 



stagnalis wasatchensis. obrussa peninsulas. pallida. 



sanctoemaris. obrussa exigua. catascopium. 



occidentalis. obrussa decampi catascopium adamsi. 



lepida. galbana. catascopium niagarensis. 



columella. petoskeyensis. daz'isi. 



columella chalybea. palustris. nasoni. 



columella casta. palustris alpenensis. woodruff. 



utahensis. palustris blatchleyi. pseudopinguis. 



megasoma. palustris desidiosa. decollata. 



haldemani. neopalustris. sumassi. 



truncatula. elodes. jacksonensis. 



doddsi. elodes jolietensis. gabbi. 



bulimoides. elodes shurtleih. emarginata. 



bulimoides cockerelli. reHexa. emarginata mighelsi. 



