^engtli. 



Breach 



13.50 



6.25 



15.00 



6.00 



14.00 



6.00 



L3.75 



COO 



12.50 



6.00 



13.50 



6.00 



12.75 



6.00 



13.50 



6.25 



284 THE CHICAGO ACADEMY OF SCIENCES. 



Breadth. Aperture length. Breadth. 



7.00 3.10 mill. Type 



6.00 3.50 " 



6.50 3.50 " 



6.50 3.25 " 



6.50 3.00 " Cotypcs 



6.50 3.00 " 



6.25 3.00 " 



6.50 3.50 " Maine 



Types : Coll. Bryant Walker, eight specimens, No. 20040 ; co- 

 types, Chicago Academy of Sciences, five specimens, No. 23968 ; Acad- 

 emy of Natural Sciences, Philadelphia. 



Type Locality : Headwaters of the Union River, Ontonagon 

 County, Michigan. 



Animal : Not differing from that of obrussa. 

 Jaw and Radula : Same as those of obrussa. 

 Genitalia: Similar to those of obrussa (Maine specimen). The 

 retractor muscle of the penis-sac differs in being much larger, fan- 

 shaped, with numerous branches at either end. (PI. XI Y, fig. G, 3.) 

 A specimen measured as follows : 



Prost. Ret. mus. Ret. mus. Rec. sem. 

 Penis. Penis-sac. Vas. def. duct. penis, penis-sac. duct. Shell. 



2.00 2.00 5.00 1.00 1.00 1.00 1.00 13.50 



Range : Northern Maine to northern Michigan. Southern Boreal 

 and northern Transition (Alleghanian) life zones. Canadian and Nova 

 Scotian regions. Further search will probably reveal this variety in 

 many other localities in the northern part of the United States. 



RECORDS. 



Maine: Unity, Waldo Co. (Berry) ; Thomaston, Knox Co. (Lermond). 



Michigan : Union River and Little Iron River, Ontonagon Co. ; Salmon 

 Trout River, Marquette Co. ; St. Mary's River, Sault Ste. Marie, Chippewa Co. 

 (Walker) ; rock pools of Middle Branch, Lake Superior, Ontonagon Co. 

 (Walker and Ruthven). 



Geological Distribution : Unknown. 



Ecology : "Occurs quite numerously in the rock pools of the 

 middle Beach." (Walker and Ruthven.) 



Remarks : This variety differs from typical obrussa in being 

 more slender, with a longer, more turreted spire, deeper sutures and 

 a more oval aperture. The body whorl is more cylindrical than in the 

 typical form. Mr. Walker says : "It is apparently characteristic of 

 the small rivers tributary to Lake Superior. With the exception of 

 a few specimens from Sault Ste. Marie, the typical form has not been 

 as yet found in the upper peninsula at all. As a characteristic local 

 form of a large region, it seems worthy of a name." The specimens 



