SUBALPINE MOLLUSCA. 75 



hinge-margin, the edges of valves meeting at an angle of 

 about 80°, not flattened nor spreading laterally; the ante- 

 rior very little lower than posterior, but slightly sharper. 

 Divergence of upper margins from umbonal apex, 80° to 

 90°. Color pale pearl-gray, sometimes iridescent, often 

 with a narrow yellowish marginal band; epidermis tinged 

 olive, wearing off in adult, surface smooth, shining; 

 growth-lines very faint, inside of shell white. Younger 

 shell more oval, beaks less prominent, the calycles in 

 shells not half grown being everted when seen from end 

 of shell, instead of inverted (fig. 7). Fry oblong-oval, 

 much compressed, its valves very distinctly seen in caly- 

 cles of adult. Soft parts yellowish, tinted with red, the 

 colors visible through shell. Length, 0.30 to 0.34 inch; 

 height, 0.26 to 0.30; diameter, 0.16 to 0.21. Fry, 0.05 

 to 0.06 long; 0.04 to 0.05 high; 0.02^ to 0.033^ thick. 



\^arieiies. Specimens vary more or less in one or more 

 of the dimensions, in the curves of the outline and in con- 

 vexity, but not over 0.05 inch. The characters of young 

 shells, as seen in the figures, are sometimes persistent in 

 adults, altering the form more or less, but as the figures 

 are three times the diameters of shells, those differences 

 are not so perceptible to the eye as shown in the figures. 



Figures 9 and 10. We have included these two spec- 

 imens for comparison, with some doubt whether they are 

 not of a different species. They were collected in Kla- 

 math Lake, Or., by Mr. A. Forrer, of Santa Cruz, Cal., 

 and kindly sent to us by Mr. E. W. Roper, of Revere, 

 Mass., who writes that in his opinion all found were im- 

 mature. They differ from S. raymondi in having a 

 thicker, brown epidermis and in higher beaks, but less 

 prominent calycles. By comparison of the beaks with 

 the young of the former (figs. 5 to 7), it will be seen, 

 however, that they are nearly mature, and in their out- 

 lines come nearer to figures 3 and 4 than to any others- 



