179 Midway Stage 65 



from beak to midway of the cardinal plateau; two cardinal teeth 

 of left valve of equal size, lunule margin extending from beak 

 downwards and outside of the anterior tooth, leaving a slight 

 crease between the two, and then continuing downward with a 

 slight inflection and forming a pseudo-lateral tooth; cardinal 

 tooth in right valve large, triangular with a pit on either side for 

 the reception of the teeth of the opposite valve; the margin of 

 the escutcheon in this valve answering for a faint posterior 

 lateral tooth; submargin generally smooth, but often crenulate 

 at some little distance in from the actual periphery of the shell. 

 This species is very abundant in the vicinity of Graveyard 

 hill, beds 15 and 16?. Its high, anteriorly located and curving 

 beaks, its broad post-umbonal slope, its hinge characters, and 

 size and general outline distinguish it from any other known 

 form. 



Localities. — Ai^abama: }^ mi. W. of Graveyard hill; i mi. N. 

 of Allenton. 



PROTOCARDIA. 



Protocardia nicolletti vzr., PI. 6, fig. 2. 



Var. of C nicolletti Con., Proc. Ac. Nat. Sci. Phila., 1841, p. 33. 

 C. nicolleti Con., Wailes' Ag. and Geol., Miss., 1854, 

 pi. 14, fig, 6. 



Conrad'' s original description of C. nicolletti. — "Cordate, ventri- 

 cose, polished, with crowded, minute, impressed radiating lines; 

 beaks central, summits very prominent; posterior margin nearly 

 direct, slightly emarginate, posterior slope with larger striae than 

 the disk, and muricated with radiating rows of approximate, 

 rather obtuse, slender and prominent tubercles. Length, 2^ 

 inches. Height the same. 



' ' For this splendid Cardiu?7t I am indebted to my distinguished 

 friend, J. N. Nicollet. It was found in green clay at 50 feet in 

 height on the right bank of the Washita river, Monroe county, 

 Louisiana." 



I am quite aware that this variety differs considerably from the 

 typical form. In brief the differences may be stated as follows: 



In the typical form the anterior and posterior dorsal margins 

 are prominent, in the variety they are obliquely truncated; in 

 adult typical forms the basal margin is often circular, in the 

 variety nearly rectilinear. 



The lyignitic specimens from Virginia and Alabama, named 

 P. lene and afterwards P. virginiana by Conrad, have the general 

 shape of this variety except that the umbones instead of being 



