SUBALPINE MOLLUSCA. 77 



height, which had been first described as species, while 

 the figure given is shorter than the type described, being, 

 hke that of S. lenticula, a rare extreme. 



S. PARTUMEiuM Say. The specimens nearest to this 

 species that we have, are figured as Nos. 12, from Worces- 

 ter, Mass. (showing hinge), and 13, 14, from Columbus, 

 Ohio. Though smaller than Prime's largest, as shown 

 in the diagram, fig. 15, they have a similar relative con- 

 vexity, and come nearer his description than his figure, 

 no other calyculate species approaching this both in size 

 and convexity. 



Figure. Length. Height. Diameter. 



Prime's type 15 0.50 0.43 0.31 



Worcester example 12 0.38 0.33 0.22 



Columbus examples 13. I4 0.37 0.33 0.21 



The two latter, however, in outline much resemble S . 

 ii'uncatum, though not subangled at the upper margin as 

 figured by Prime, and are perhaps nearer to the next 

 mentioned species. 



S. SECURis Prime, figs. 20 and 21. The shells we se- 

 lect to represent this form are from Plattsburg, N. Y., 

 the largest being very closely like Prime's type in out- 

 line, while the convexity is proportionately the same, as 

 shown by the diagram of Prime's type, fig. 16. 



It is evident from a comparison of Prime's descriptions, 

 that figures 46 and 47 ( S. contractiwi), on p. 49 of his 

 Monograph, have been accidentally transposed by the 

 printers, which is confirmed by inspecting his first figure 

 of S. securis in the Annals N. Y. Lyceum of N. H., Vol. 

 V, PI. vi, where a smaller one is figured. 



Fig. 46 being S. securis, is represented as differing 

 from S . triincatum chiefly in greater convexity, and the 

 variety cardissa was described by Prime as a still more 

 rounded form, connected by gradations. As is shown 

 by the diagram, the convexity of Prime's type is relative- 



