78 CALIFORNIA ACADEMY OF SCIENCES. 



ly the same as that of his "<5. partumeiuui ,'' and from 

 the connecting links shown by our figs. 12, 13, 14, as 

 well as its limitation to the northern tier of States, it 

 seems most probable that S . secnn's is only a stunted va- 

 riety of S. fartiimeinm Say. The same error of using 

 the figure of S. contractum for that of S . secnn's is copied 

 by Binney in his edition of Invert, of Massachusetts. 



Figure. I<ength. Height, Diameter. 



Prime's type i6 0.37 0.31 0.25 



Plattsburg- examples 20,21 0.28 0.24 0.15 



S. TRUNCATUM Liuslcy, figs. 22, 23, 24, 25. These are 

 selected specimens having the least convexity of any, out 

 of numerous similar forms from several Eastern States, 

 these agreeing best with Prime's description. They are, 

 however, all smaller, less rhomboid and subangled, more 

 convex and more rounded than his type which represents 

 apparently a rare extreme in form, while many occur 

 more or less intermediate. 



Diagram, fig, 17, represents the convexity given by 

 Prime for truncatum, a flatness not seen by us in any of 

 numerous specimens, and closely agreeing with that he 

 assigns to S. lenticnla (fig. 18), which he says is "so 

 similar in nearly every respect to S . truncatu?n that it is 

 difficult to tell them apart." It appears, however, from 

 later specimens of S . lenticnla that it is quite as closely 

 connected with S. ■partnmeinm (see notes, p. 76), and it 

 follows that all four so-called species may yet be com- 

 bined under the last name, or rank only as subspecies. 

 It is possible that the flattest forms represent in all cases 

 the most northern grown specimens. 



Figure. Length. Height. Diameter. 



Types of Prime 17 0.37 0.31 0.15 



Baldwitisville 22 0.29 0.24 0.14 



Baldwinsville (Fry) 23 0.03 0.02 J^ o.oiK 



Michigan (Young) 24 0.19 0.16 0.12 



Readville, Mass 25 0.32 0.25 0.15 



