COMPOSITA 495 



clearly being an athyroid shell of the genus Composita. The species 

 may be easily distinguished from any other member of this genus by its 

 subtriangular form, with its greatest breadth near the front of the shell, 

 by the acutely angular antero-lateral extremities of the shell, and by the 

 three distinct emarginations of the front. 



The exact horizon of the species can be certainly determined only by 

 the collection of additional examples from the type locality at Burlington, 

 Iowa. The original definition gives the horizon as "Chemung Group", 

 which would indicate Kinderhook. The shell itself is from a limestone 

 and its lithologic characters would suggest that it was collected from 

 the uppermost bed of the Kinderhook at Burlington. 



Horizon. Upper Kinderhook (?). 



COMPOSITA ? CORPULENTA (Winchell) 

 Plate LXXVII, Figs. 55-59 



1863. Spirigera corpulenta Winchell, Proc. Acad. Nat. Sci. Phil., p. 6. 

 1900. Athyris corpulenta Weller, Trans. St. Louis Acad. Sci., vol. 10, p. 75, 

 pi. 2, figs. 12-15. 



Description. Shell of medium size or smaller, subglobose in form, 

 longer than wide, the width and thickness subequal, longitudinally sub- 

 elliptical in outline, the greatest width near the mid-length of the shell, 

 the hinge-line very short, the cardinal extremities rounded. The dimen- 

 sions of a nearly perfect specimen are : length 17 mm., width 13.5 mm., 

 thickness 13 mm. 



Pedicle valve strongly convex or ventricose, the greatest convexity 

 near or a little posterior to the middle, the surface curving abruptly in 

 all directions from the point of greatest convexity; the beak contiguous 

 with that of the opposite valve, with no indication of a foramen in any 

 of the specimens examined ; no cardinal area developed and the characters 

 of the delthyrium riot shown in any of the specimens ; mesial sinus obscure 

 or obsolete, when present consisting usually of a mere flattening of 

 the surface along the median line originating near the middle of the valve, 

 which sometimes becomes slightly concave anteriorly. 



Brachial valve a little less convex than the pedicle, the point of greatest 

 convexity near or posterior to the middle, the surface curving steeply 

 from the highest point to the posterior and lateral margins, and more 

 gently to the anterior margin; the beak incurved beneath that of the 

 opposite valve ; the mesial fold not differentiated. 



Surface of both valves marked by concentric lines of growth which 

 are crowded at intervals. 



Remarks. The generic relations of this species are not clearly estab- 

 lished. The species has been observed only in a fine-grained sandstone in 

 such condition of preservation that the internal characters cannot be 



