136 THE NAUTILUS. 



It is quite different from any other species found in the State, but in 

 present chaotic condition of the synonymy of this genus it does not 

 seem advisable to run any risk of duplicating some previous descrip- 

 tion. 



Planorbis lentus Say. Cited by Miles, who probably had a large 

 form of trivolvis before him. 



P. trivolvis Say. Abundant everywhere. P. corpulentus Say and 

 regnlaris Lea usually referred to this species are cited as distinct by 

 DeCamp. The latter is doubtfully cited by Currier. 



Specimens exhibiting the distorted appearance caused by a change 

 of plane in the growth of the whorls as described by Ingersoll in his 

 P. plexata occur not infrequently in some localities. 



P. truncatus Miles. This peculiar and well marked form appears 

 to be confined to Michigan. Described originally from specimens 

 collected from Saginaw Bay, it seems to have escaped further notice 

 until 1887, when it was discovered in the Elk river, Antrim County. 

 These specimens are quite typical and not only confirm the validity 

 of the species, but extend its range across the entire northern part of 

 the State. 



P. hicarinatus Say. Common everywhere. 



P. bicariiiaius corrugatiis Curvier. Perch Lake, Kent County. A 

 well marked form characterized by its costate surface. Specimens 

 from Long Lake, GrandTraverseCounty, exhibit the same tendency 

 but not to the extent shown by the shells from the original locality, 



P. hicarinatus major. Specimens from Crystal Lake, Benzie 

 County, from their perfection and size are worthy of being separately 

 noticed. They are larger, pinkish-white in color, with the carinseon 

 both surfaces elevated into a keel which is white. The superior 

 carina extends to the lip and modifies the shape of the aperture, 

 which is a more or less expanded and darker in color within. The 

 outer lip is somewhat thickened and white. 



P. multivolvis Case. The rediscovery of this long lost species by 

 Dr. M. L. Leach, in Marl Lake, Roscommon County, has been 

 recorded in the Journal of Conchology, V, p. 330. The hump on 

 the last whorl opposite the aperture as figured in Land and Fresh- 

 Water Shells pt. II, fig. 186, is not a characteristic of the normal 

 shell, as but a small percentage of several hundred specimens 

 exhibit any tendency toward it. When it does occur, it bears the 

 appearance of being an abnormal extension of the last whorl being 



