412 THE CHICAGO ACADEMY OF SCIENCES. 



tractors meet in the columellar muscle where they form one attach- 

 ment; frequently this attachment is split into two branches; protrac- 

 tor muscles normally five in number, two anterior and three posterior, 

 the former being the largest and attached to the penis-sac by many 

 small branches; vas-deferens 23.00 to 25.00 mill, in length; prostate 

 duct 6.00 mill, in length enlarging slightly as it joins the prostate; pros- 

 tate very large, flattened, elongated, squarely rounded anteriorly, grad- 

 ually tapering posteriorly to form the long, narrow part which joins 

 the uterine portion of the oviduct. 



Female Organs: Receptaculum seminis large, rounded, its duct 

 6.00 mill, long; first accessory albuminiparous gland large, elongate, 

 pear-shaped; the lower portion of the oviduct is rather long and 

 narrow. 



The musculature of the penis varies somewhat in different speci- 

 mens; in two individuals from Isle Royale, Michigan, the distal end 

 of the posterior protractor had shifted its position so that it became a 

 second, inferior penis-sac retractor. (PI. XV, fig. B, 1, 2) ; this was 

 noted also in a specimen of emarginata mighelsi from Maine. The 

 cause of this shifting of muscles was not ascertained. 



The measurements of the genitalia of specimens from Aroostook 

 Co., Maine, and from Isle Royale, Michigan, are tabulated below. 

 (Dissections No. 23661, 23662, 23663, 23664, 23666.) 



Penis- Penis Penis- Vas. Prost. Rec. 



Penis. sac. ret. sac. ret. def. duct. sem. Shell. 



2.00 4.50 1.75 1.50 23.00 6.00 6.00 18.50 Maine. 



2.10 4.25 2.25 2.25 25.00 6.00 6.00 22.00 



2.00 4.50 2.00 2.00 24.00 6.00 6.00 21.00 



2.75 2.50 1.75 1.00 16.00 4.75 7.75 16.00 Michigan 



2.00 2.00 2.00 1.85 12.50 4.75 7.75 



It will be noted that the Isle Royale specimens have a shorter 

 penis-sac, a shorter vas deferens and prostate duct and a longer recep- 

 taculum seminis duct. The shells of the latter are smaller and the 

 spire more pointed than the shells from Maine. The form and posi- 

 tion of the different organs were generally the same in both lots. 



RANGE: (Figure 46). Maine to western Ontario, south to the 

 northern part of the southern peninsula of Michigan, and northern 

 New York. 



Typical emarginata appears to be a species of northern distribu- 

 tion, principally confined to the Boreal (Canadian) life zone and to 

 the Canadian and Nova Scotian regions. No specimens of the typical 

 form have been seen from outside this area. The range will doubt- 

 less be much extended when the typical form is differentiated from 



