MOLLUSCA OF MICHIGAN— WALKER. 



465 



Mesodon'albolabris, Currier, Shell-bearing Moll. Mich., 5, (1868). 



^ DeCamp, Shell-bearing Moll. Mich., 6, (1881). 



Pohjgyra , Walker, Rev. Moll. Fauna Mich., 16, (1894). 



fV 



Fig. 12. Var. dentaia. (Binney.) 



-i- Var. DENTATA Tryon. 



Parietal wall with a slight denticle. 

 Mesodon albolabris dentata, Tryon, Am. Jour. Con. III., 



39, pi. vii., fig. 6, (1867). 

 ■ — , Currier, Shell-bearing Moll. 



Mich., 5, (1868). 

 , DeCamp, Shell-bearing Moll. 



Mich., 6, (1881). 

 Polygyra , Walker, Rev. Moll. Fauna 



Mich., 16, (1894). 



Fig. 13. Var. maritima. 

 (Pilsbry.) 



Helix albolabris maritima 

 Polygyra 



Var. MARITIMA (Pilsbry.) 



Shell smaller, surface very distinctly and beautifull}^ 

 decussated by spiral and oblique lines. Base notably 

 swollen near the umbilicus, back of the lip. 



Alt. 12-17, diam. 18i-24i mm. 



Pilsbry, Proc. A. N. S. P., 1890, 283, fig. 

 Walker, Rev. Moll. Fauna Mich., 16, (1894). 



traversensis/' Leach./' Pilsbry, Man. Con. IX, 76, (1894). 

 minor, Sterki, L. & F. W. Moll. N. Phila, 4, (1894). 



— , Walker, Rev. Moll. Fauna Mich., 16, (1894). 



Abundant over the entire state, and exhibits great variation in size, color 

 and thickness of the shell. Deeply colored examples when fresh, frequently 

 have the lip tinged with light purple, which, however, fades out gradually, 

 especially when exposed to the light. The dentate form occurs not infre- 

 quently associated with the type. It is, perhaps, questionable whether the 

 true var. maritima occurs in this state. The shells from Traverse City, 

 called var. traversensis by Leach, but never formally described, are very 

 similar, but not quite typical, lacking the swollen base characteristic of the 

 New Jersey form. They seem to be intermediate between the true mari- 

 tima and the form described by Sterki as var. minor. The same form has 

 been found at Grand Rapids, and occurs in many localities in the sandy 

 districts in the western and northern parts of the state. It is an interesting- 

 coincidence, if nothing more, that this form first discovered in the sandy 

 regions of New Jersey, should reappear under similar environmental condi- 

 tions in Michigan, and be accompanied by a fluviatile form (Lymncea gal- 

 bana Say), which, until found here, was considered extinct and pecuhar to 

 the recent deposits in New Jersey. 



Taking all the material now accessible into consideration, it does not seem 

 feasible to separate the several forms known as maritima, traversensis and 

 minor into distinct varieties. As a w^hole they seem to be a well marked 

 depauperate race, the result of unfavorable conditions of environment and 

 characteristic of the sandy regions of the northern and western counties. 

 But they vary in size and contour quite as much as the typical form and 

 grade insensibly into each other and into it. At present therefore, it would 



