294 MISSISSIPPIAN BRACHIOPODA 



Remarks. This species of Spiriferina may be recognized by its prom- 

 inent umbo, strongly incurved beak of the pedicle valve, strongly arched 

 cardinal area, and especially by the median plication of the fold and 

 sinus. Both the plications and concentric markings are somewhat 

 coarser than the same features in 8. subtexta. In no case have the con- 

 centric lamellae given evidence of being fimbriate upon any of the speci- 

 mens observed, as is the case in 8. subtexta, but this is a character which 

 is easily destroyed and the shells may have possessed it when living. The 

 punctate structure of the shell is commonly obscure or indeterminable 

 upon the specimens, but occasional examples, exfoliated wholly or in part, 

 show the presence of the perforations. 



Horizon. Kinderhook. 



SPIRIFERINA SUBELLIPTICA (McChesney) 



Plate XXXVI, Figs. 54-57 

 1860. Spirifer subelliptica McChesney, Desc, New Pal. Foss., p. 43. 



1894. Spiriferina subelliptica Hall and Clarke, Int. to Study of Brach., 



pt. 2, pi. 2, fig. 2. 



1895. Spiriferina subelliptica Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 



pi. 35, figs. 21-22. 



Description. Shell of medium size or somewhat larger, transversely 

 subelliptical in outline, the hinge-line shorter than the greatest width of 

 the shell, the cardinal extremities rounded, the greatest width posterior 

 to the mid-length. The dimensions, subject to error, of a nearly com- 

 plete but somewhat crushed specimen, are: length of pedicle valve 19.5 

 mm., length of brachial valve 17 mm., greatest width 28.5 mm., thick- 

 ness estimated 12 mm., length of hinge-line 22.5 mm., height of cardinal 

 area 3.5 mm., width of sinus in front 11.4 mm. 



Pedicle valve most prominent towards the umbo, compressed toward 

 the cardinal extremities ; mesial sinus sharply defined, non-plicate, origin- 

 ating at the beak, of moderate depth and rounded in the bottom; beak 

 rather small, pointed and incurved; cardinal area moderately high, eon- 

 cave with the curvature increasing towards the beak, sometimes the 

 surface of the area rounds into the lateral slopes of the valve with but a 

 slight limiting ridge, but more often the lateral margins are well defined ; 

 delthyrium rather large, as high or higher than wide; each lateral slope 

 marked by from seven to eleven simple, rounded plications which 

 originate near the cardinal margin and grow successively smaller towards 

 the cardinal extremities, the last two or three sometimes being very 

 faint. Internally the shell is much thickened in the apical region, a 

 strong median septum is present which reaches to about the middle of 

 the valve, the dental plates are strong and short, the muscular scars are 

 rather small and only moderately distinct. 



