INVERTEBRATES. 



153 



In first describing this species, we regarded it as a variety of A. piriformis, 

 Shumard, for which we proposed the name rudis. not being aware at that time 

 that Prof. Hall had used that name for another species in his Supplement to 

 the Iowa Report. Later comparisons, however, led us to the conclusion that it 

 is specifically distinct from Dr. Shumard's A. piriformis, and as the name A . 

 rudis could not be retained for it, we proposed to call it A. pistilliformis. It 

 differs from A. piriformis, Shumard, in the subspiniferous character of its 

 plates, and in the possession of only two or three interradial plates, instead of 

 six in each interradial space. It also differs in having a more ventricose 

 dome, while the inferior half of its body is more abruptly contracted below the 

 arms. 



Locality and position: Salt-Lick Point, Marion county, Illinois; Kinderhook 

 group, of the Subcarboniferous series. 



MOLLUSCA. 

 BRACHIOPODA. 



Genus RHYNCHONELLA, Fischer, 1809. 



(Mem. Soc. Imp., Moscou, ii.) 



Rtnchonella missouriensis, Shumard. 



PI. 14, Fig. 4 a, 4b. 



Rhynchonella Missouriensis, Shumard, 1855. 2d Ann. Rep. Geol. Survey Missouri, p. 

 204, pi. C, fig. 5 a. 



Shell subtrigonal, subglobose or moderately gibbous ; late- 

 ral margins rounded; front somewhat truncated, or a little 

 sinuous in outline ; postero-lateral margins converging to the 

 beaks at an angle of about 114°. Dorsal valve more convex 

 than the other, sometimes very gibbous;-mesial elevation rather 

 obscure, rarely extending beyond the middle of the valve, 

 occupied by from two to three (rarely four) rounded plica- 

 tions, which generally become obsolete near the middle of the 

 valve ; anterior margins on each side of the mesial ridge pro- 

 vided with one or two obscure plications ; beak not prominent. 

 Ventral valve moderately convex in the umbonal and antero- 



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