372 MISSISSIPPIAN BRACHIOPODA 



the smaller individuals but in the larger ones marked by a more or less 

 obscure median plication which originates near the middle of the valve. 



Braehial valve less convex than the pedicle, its greatest convexity pos- 

 terior to the middle, the surface curving abruptly to the cardinal margin, 

 sloping with a gentle convex curvature to the antero-lateral margins, a 

 little compressed towards the cardinal extremities; mesial fold narrow, 

 defined to the beak, rounded, barely elevated above the general surface 

 of the valve, smooth in all of the examples observed; lateral slopes 

 marked by plications similar in form and number to those of the opposite 

 valve. 



The minute surface markings of the shell are not shown on any of 

 the specimens observed because of their condition of preservation, but a 

 few concentric lines of gro\vth are usually recognizable. 



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

 casts and natural moulds of the exterior, in a fine-grained sandstone. In 

 the internal casts the beak of the pedicle valve is always obtuse and more 

 or less truncated, indicating a notable thickening of the shell in that re- 

 gion. A few natural moulds of the exterior have been observed, from 

 which artificial casts of the beak and cardinal area have been secured, 

 which show the external form of that portion of the shell. In the dimen- 

 sions of the small, complete, internal cast given above, the length of the 

 pedicle valve is materially less than it would be were the shell itself pre- 

 served. The total length of the other specimen whose dimensions are 

 given is estimated from a cast from a natural mould of essentially the 

 same size. The species is a very distinct one, but it more closely resem- 

 bles 8. chouteauensis than any other, it may be distinguished from that 

 species, however, by the proportionately more elongate shell, the shal- 

 lower and narrower mesial sinus which is either smooth or is marked 

 only by an obscure mesial plication and never by lateral ones branching 

 off from the inner margins of the bounding plications. 



Horizon. Kinderhook. 



Plate LII, Figs. 5-11 



1909. Spirifer fernglensis Weller, Bull. Geol. Soc. Amer., vol. 20, p. 306, 

 pi. 13, figs. 9-10. 



Description. Shell small, wider than long, subglobular in form, hinge- 

 line a little shorter than the greatest width of the shell, cardinal ex- 

 tremities rounded. The dimensions of a nearly perfect specimen are: 

 length of pedicle valve 13.5 mm., length of brachial valve 11 mm., width 

 14.6 mm., length of hinge-line 13 mm., thickness 11 mm., width of mesial 

 sinus in front 5.2 mm. 



