10 



Gonyodiscus shimekii (Pilsbry 1890) 

 Plate I, figure 8 



1890. Zonites shimekii Pilsbry, Nautilus, vol. 4, p. 3. 



1890. Zonites shimekii Pilsbry, Proc. Acad. Nat. Sci. Phila., 1890, p. 



297, pi. 5, f. 9-11. 



1891. Zonites shimekii Pilsbry, Nautilus, vol. 5, p. 39, pi. 2, f. 9-11. 

 1898. Zonitoides shimekii Pilsbry, Nautilus, vol. 11, p. 131 (merely 



catalogued). 



1901. Pyramidula shimekii Shimek, Bull. Lab. Nat. Hist. State Univ. 

 Iowa, vol. 5, p. 139. 



Material Examined 



It is a considerable surprise to find this species, heretofore known, in 

 the living state only by the subspecies cockerelli Pilsbry which is an in- 

 habitant of the southern Rockies flourishing so far north and in such num- 

 bers, especially since neither it nor cockerelli has yet been encountered in 

 Montana, whereas typical shimekii was originally described as a fosssil 

 from the Iowa Loess. The writer has had no opportunity of examining 

 any Iowa shimekii, but upon comparison with cockerelli from Elorado, 

 Colorado, sent him by Junius Henderson, the Albertan shells prove to 

 run a little larger, are lighter and greyer in colour, are more robust, and 

 seem thicker shelled, and the axial ribs on the upper surface of the whorls are 

 more even, more sharply cut, and probably more numerous. Examples 

 of cockerelli from Colfax county, New Mexico, collected by Ashmun, are 

 rather different in appearance from either the Coloradan or Albertan shells. 

 The possibility was considered that the Canadian specimens represent a 

 new subspecies, but, firstly, there seemed too little comparative material 

 available to render such an opinion safe, and secondly, it was thought 

 possible that a similar relation might exist between the Albertan race and 

 the typical Loess form to that suggested by Pilsbry (1916, p. 857) for Oreo- 

 helix cooperi stantoni (Dall) of southwestern Saskatchewan and the Loess 

 0. c. iowensis (Pilsbry). Thereupon a few of the present specimens were 

 sent to Dr. Pilsbry, with the request that he compare them directly with 

 the types of both shimekii and cockerelli. He replied (November 24, 1920) 

 as follows: "The P. shimekii from Canada are about intermediate be- 

 tween typical shimekii and cockerelli. The last should have a noticeably 

 wider umbilicus. In your shells the umbilicus is equal to that of the most 

 openly umbilicate of the original shimekii. The distinction of the race 

 cockerelli is probably of doubtful expediency, though usually it is more 

 depressed and more open beneath." It, therefore, seems reasonable to 

 refer the Albertan race outright to shimekii, whether or not one follows 

 Shimek (op. cit., pp. 140-143) in reducing cockerelli to the synonymy. 



