OF DENISON UNIVERSITY 
77 
Our specimen gapes posteriorly and below, but probably the edges 
naturally apply all around. Greatest convexity upon the post umbo- 
nal ridge about one-fourth the distance from the beak to posterior 
angle. A shallow sinus extends from the umbo to the middle of the 
lower margin. Length 31 mm, height 22 mm, thickness 14 mm, beak 
about 7 mm, from anterior margin, hinge 23 mm. Allorisma layer, 
below congl. II, at Newark and Rushville. Not having access to 
Prof. Hall’s description, I am unable to make direct comparisons, but 
have no doubt that this is the species in question. The comparison 
with E. tapesiformis, Meek, reveals many differences, that species also 
seems to come from a different horizon. 
Edinondia hurlingtonensis, W. and W. 
(Plate IX, Fig. 27, Fig. 17 (.^); Plate IV, Fig. t8. ) 
Our species is doubtless the one generally identified with E. bur- 
lingtonensis and Prof. Winchell has made direct comparison of our 
forms with Iowa types and sustains the identification. There is, how- 
ever, a wide range of variation in specimens on the same slab, the 
majority being almost like E. radiata, H., in form. The original de- 
scription runs as follows : 
“ Shell of medium size, broadly subelliptical in outline, with reg- 
ularly ventricose valves, breadth equal to three-fifths of the length. 
Beaks situated within the anterior third, strong, prominent, and in- 
curved. Hinge-line and basal margin gently and equally curved ; an- 
terior and posterior extremities broadly and equally rounded. Surface 
marked by numerou-s strong, concentric undulations, parallel to the 
margin of the shell. In full-grown individuals there is a shallow, un- 
defined sulcus, commencing near the centre of the shell, and reaching 
the border near the middle of the base.” “ Differs [from E. radiata] 
in having the posterior extremity narrower than the anterior, instead 
of much broader; and also in the concentric undulations.” 
After an examinadon of perhaps fifty specimens, all from the 
same bed within a few inches of each other (vertically), we observe 
the following nearly constant differences. The posterior part of the 
shell is higher than the anterior ; sulcus well-defined ; posterior mar- 
gin much more broadly rounded than the anterior and obliquely sub- 
