358 MISSISSIPPIAN BRACHIOPODA 



wards the cardinal extremities ; mesial sinus shallow, narrow, rounded in 

 the bottom, ill-defined laterally, marked by from 6 to 10 plications similar 

 in every respect to those upon the lateral slopes. 



Brachial valve less convex than the pedicle, its depth usually not more 

 than one-half that of the pedicle valve, its surface is gently convex across 

 the middle portion, but curves abruptly to the lateral margins and to the 

 cardinal margin, sometimes a little compressed towards the cardinal ex- 

 tremities; the mesial fold is depressed, being scarcely elevated above the 

 general surface of the valve in its posterior half, it is rounded in contour 

 and ill-defined laterally, it is marked by plications similar in form and 

 number to those of the opposite valve. 



The minute surface markings are not preserved in the casts, but the 

 presence of concentric lines of growth are indicated which become 

 crowded near the anterior margin 



Remarks. This species has been observed only in the form of easts in a 

 fine-grained yellow sandstone. It may be distinguished from S. subrotundus, 

 the species which it most closely resembles, by its more elongate form, 

 its shallower fold and sinus, its flatter plications, and by the lateral 

 compression of the shell. The surfaces of the lateral slopes of the two 

 valves of S. subrotundus meet at the lateral margins of the shell in an 

 acute angle while in this species the angle is at most obtuse and is usually 

 absent because of the inflection of the lateral margins of the valves to 

 form a flattened area towards the cardinal extremities. The peculiar 

 elongate form of the species, with its completely plicated shell and shal- 

 low fold and sinus, resembles in some degree the elongate, short-hinged 

 varieties of the Devonian species, S. Jnmgerfordi. The species also resem- 

 bles in its elongate form and general proportions, the Russian species 8. 

 mcsquensis Fiseh., but does not grow so large as that species. The re- 

 lationships of neither this species nor 8. subrotundus with the completely 

 plicated Spirifers of the 8. striatus type, represented in American faunas 

 by 8. grimesi and S. logani, can be determined, since the minute longi- 

 tudinal stria? of those species cannot be detected on specimens preserved 

 as these are. 



Were the shell itself preserved in this species, it is not improbable that 

 a larger number of plications would be shown ; in the condition of preser- 

 vation of the specimens about 50 plications can usually be detected about the 

 margin of the shell, including those on the sides and in the fold and sinus, 

 they grow faint and disappear before reaching the cardinal extremities, 

 and on the shell surface itself as many as ten or more additional ones 

 would probably be seen. 



Horizon. English River grit of the Kinderhook. 



