Subfamilies, Genera, and Subgenera — Recent and Fossil 153 



and spade-shaped. The ectocone is modified to form three small cusps. The 

 outer marginal teeth (20) are simply serrated and much smaller than the 

 earlier marginal teeth. 



The races icisconsine?ise and canadense (figs. 2, 3) differ little in their 

 radulae from typical canipanidatum. H. campamdatum smithi is also 

 similar (fig. 4), the lateral teeth showing a gradual change in the form of 

 the mesocone. The teeth 6-9 might all be called intermediate, since the 

 mesocone is alike in all. Smithi has a larger tooth formula than any of the 

 other races of campanulatum. The radulae of the subgenus Planorbella are 

 in all respects like those of Pierosoma. 



The formulae of the different races are shown in the table below: 

 Race Formula Locality 



campanulatum 20-1-20 to 22-1-22 Oneida Lake, New York 

 c. wisconsinense 21-1-21 to 22-1-22 Muskelhinge L., Wisconsin 



c. wisconsinense 21-1-21 North Star Lake, Wisconsin 



c. canadense 21-1-21 to 23-1-23 Sturgeon L., Ontario 

 c. canadense 21-1-21 to 23-1-23 Basswood R., Ontario 

 c. smithi 26-1-26 Doughis L., Michigan 



Helisoma campanulatum wisconsinense w^as also studied anatomically 

 from Lake Nipissing, Ontario. 



Geographical Distribution. Planorbella has been collected from Great 

 Slave Lake, Labrador, Quebec, and Ontario south to New York, Ohio, and 

 Illinois. Westward it extends to North Dakota and Nebraska. It is essen- 

 tially a group of the northern part of the LTnited States and Canada. In 

 this area it varies considerably and several races have been recognized. 

 These appear to be mostly local races, not geographical, possibly environ- 

 mental variations. 



Species Considered as Valid. The following species and races are 

 recognized: 



Helisoma (Planorbella) campanulatum Helisoma (Planorbella) campanulatum 



campanulatum (Say) michiganense F. C. Baker 



Helisoma (Planorbella) campanulatum Helisoma (Plane/rbclla) campanulatum 



wisconsinense (Winslow) rudentis (Dall) 



Helisoma (Planorbella) campanulatum Helisoma (Planorbella) campanulatum 



davisi (Winslow) smithi (F. C. Baker) 



Helisoma (Planorbella) campanulatum Helisoma (Planorbella) multivolvis 



canadense F. C. Baker (Case) 



Helisoma (Planorbella) campamdatum 



collinsi F. C. Baker 



Geological Distribution. Pleistocene to Recent fauna. 



Remarks. Except for the campanulate aperture of the shell there is 

 nothing in the anatomy to separate Planorbella from Pierosoma. The 

 genitalia, with the long penial gland duct and the cup-shaped penial gland, 

 the pseudobranch, and the kidney are all like these organs in Pierosoma. 

 The radula is also the same. The shape of the shell, with its closely-coiled 

 whorls and particularly the bell-shaped form of the aperture, may be 

 features characteristic enough to retain Planorbella as a subgenus of 

 Helisoma. 



H. Adams has erected the group Adula (preoccupied) to admit the very 

 peculiar Planorbis multivolvis Case, a species living in Howe Lake, Mich- 

 igan. As the race collinsi of Helisoma campamdatum approaches this 

 species in the form of the shell, it would appear that the group name is 

 without value in nomenclature. Lindholm (1927) coined a new name, 



