LYMN^ID^E OF NORTH AMERICA. 157 



is generally tightly closed, but in some specimens there is a small 



chink; sculpture usually strong. Nuclear whorls as in stagnalis ap- 

 pressa. 



Aperture 



Length. Width. length. Width. 



33.00 18.50 20.00 11.00 mill. Michipicoten Island. 



50.00 30.00 32.00 22.00 " higleyi. 



42.00 27.00 27.00 19.00 " 



38.00 22.00 25.00 17.00 " '.' (type). 



49.50 29.50 32.00 17.50 " Siskowit Lake. 



45.50 27.00 31.50 17.00 " 



32.50 17.00 19.50 10.50 " Sault St. Marie. 



34.50 18.50 21.00 11.50 " 



34.00 20.00 22.00 13.00 " 



31.75 21.00 20.00 13.00 " 



Types : Sanctcemarice, 2 specimens, No. 2682, Coll. Bryant 

 Walker ; higleyi, 1 specimen, No. 23050, Coll. Chicago Academy of 

 Sciences; cotypes, Coll. J. H. Ferriss. 



Type Locality: Sanctcemarice, Neebish Rapids, St. Mary's 

 River, Michigan ; higleyi, Michipicoten Island, north shore Lake Su- 

 perior. 



Animal : Similar to stagnalis appressa. 



Jaw (PI. VI. fig. B) : Superior jaw higher than stagnalis ap- 

 pressa, with a more acute central swelling; lateral jaws not differing 

 from those of stagnalis appressa. 



Radula : Similar to that of stagnalis, but with eighteen laterals, 

 the intermediate teeth beginning on the nineteenth tooth. 



Genitalia: Similar in general to that of stagnalis appressa, but 

 differing in details of the penis retractors. (PI. XIV, fig. B.) The 

 penis retractor, instead of being inserted in the penis-sac retractor, 

 as in appressa (pi. XIV. fig. A) is inserted in the columella muscle 

 close to the insertion of the penis-sac retractor. In addition, there 

 are two or three short muscles connecting the penis retractor with 

 the penis-sac retractor. In one specimen the penis-sac retractor was 

 split to form two muscles, the lower muscle being very heavy, with 

 many insertions at its juncture with the penis-sac. (B, 2.) A speci- 

 men from Sault Ste. Marie had the two retractors fused to form a 

 broad band of tissue for about half their length to the insertion in 

 the columella muscle. All of the muscles of the male system in 

 sanctcemarice are heavier than those of stagnalis appressa. 



Some characteristic measurements of the genitalia are given in the 

 table below (dissection No. 23919) (Sault St. Marie) No. 23918 (Sis- 

 kowit Bay) : 



