1 88 1.] The Paleontologist. 43 



their more sharply defined, and rather more distant concentric micro- 

 scopic Hnes." 



Since the above quotation was pubhshed, the writer has found a num- 

 ber of other good characteristic specimens, the examination of which 

 convinces him that the species is distinct from 5. filitcxta and others. 

 The large specimens are thinner and lighter than the large ones of 

 filitexta, the cardinal area not so broad, cardinal line, generally, more 

 extended, and the shell more deflected at the extremities ; surface striae 

 less strong, and the concentric lines finer and more distinct ; the ventral 

 valve more convex on the umbone, and more deeply concave near the 

 middle ; the dorsal valve more depressed on the umbone, and more 

 highly convex near the middle. 



Position and locality : Upper part of the Cincinnati Group, near Blan- 

 chester, Clinton county, O., and other places at the same horizon. 



Streptorhynchus approximata, James. 



Strophomena approximata, James (Catalogue of Lower Silurian Fossils, 

 Cincinnati Group, Sept. 1871). 



StreptorJiynclms approximata, James (revised ed. of same catalogue, 

 April, 1875). 



Shell, resupinate ; sub-triagonal in outline ; greatest breadth at or a 

 little below the hinge line, where the shell is deflected ; lateral margins 

 rounding to the front, which may be slightly produced ; cardinal area of 

 the dorsal valve narrow ; cardinal line straight to the deflected ex- 

 tremities ; cardinal area of the ventral vdXwe flat, and about two lines wude 

 at the prominent beak, narrowing quite rapidly to the lateral points, and 

 standing at an angle of 70 or 80 degrees to the other valve, with a strong 

 prominent deltoid elevation at the middle. Dorsal valve flat on the um- 

 bone and convex toward the front, then sloping quite rapidly to the 

 free margins. Ventral valve flat or a little convex forward of the beak, 

 concave at the middle, then rising rather abruptly to the lateral and 

 front margins. Both valves covered with rather coarse, rounded, more 

 or less sinuous, radiating strice, which increase in number, by implanta- 

 tion toward the free margins, and are crossed by fine concentric raised 

 lines, More or less of rather inconspicuous wrinkles along and at right 

 angles with the cardinal line on both valves. Interior not observed. 



The largest specimen used for this description, is nearly two inches 

 broad just below the hinge line, and one and a quarter inch from the 

 point of the beak of the ventral valve to the front margin. 



This species bears some resemblance to S. filitexta, Hall ; but it is 

 more angular in outline, more convex, and in other features it appears to 

 be quite different. 



The type specimen of this species was found in the upper part of the 

 Cincinnati Group, Dearborn county, Ind. 



