210 MISSISSIPPIAN BRACHIOPODA 



shell strong, becoming much fainter towards the postero-lateral margins, 

 mostly simple, and becoming obsolete near the beak where the umbonal 

 region for a short distance is essentially nonplicate, the plications are 

 subangular on top and are separated by broad furrows. 



Brachial valve depressed convex, similar in form to the pedicle, the 

 surface gently arched from the beak to the anterior and antero-lateral 

 margins, not so much flattened anteriorly as the opposite valve, the 

 postero-lateral margins abruptly deflected to meet the similar deflected 

 portions of the opposite valve and to form a part of the subovate flattened 

 regions on each side of the. beak; mesial fold obsolete; beak small, 

 pointed, incurved beneath that of the opposite valve; plications entirely 

 similar to those of the opposite valve. 



The minute surface markings consist of extremely fine, radiating 

 striae. Lines of growth of varying strength occur at intervals. 



Remarks. This shell is allied to E. caput-tcstudinis, but it differs from 

 that species in its much smaller size and less convex valves. These char- 

 acters might be interpreted as youthful characters, but the type specimen 

 has all the appearances of being a mature shell. The species also differs 

 from R. gibbosum in its smaller size and in the absence of the conspicuous 

 divarication of the plications. It is perhaps most closely allied to R. 

 ovatum, but it is narrower, much mSore elongate, and proportionally 

 thinner. 



Horizon. Pierson limestone of the Kinderhook. 



BHYNCHOTETRA MISSOURIENSIS n. sp. 

 Plate XXVIII, Figs. 1-8 



Description. Shell of about medium size, triangularly subovate in out- 

 line, longer than wide, the greatest width anterior to the middle, the 

 postero-lateral margins nearly straight or a little concave, the antero- 

 lateral margins rounded, the anterior margin gently convex or sometimes 

 subtruncate. The dimensions of a nearly complete specimen are: length 

 of pedicle valve 29 mm., length of brachial valve 27.5 mm., width 27 mm., 

 thickness 15.7 mm-. 



Pedicle valve depressed convex, the surface gently and nearly regularly 

 convex longitudinally from beak to front, and also transversely along 

 the line of maximum width; along the postero-lateral margins the valve 

 is abruptly deflected towards the opposite valve to form a minor portion 

 of the suboval, flattened or somewhat concave, lateral regions lying upon 

 each side of the beak ; mesial sinus obsolete ; beak small, pointed, only 

 slightly incurved; plications broad, rounded, separated by rounded fur- 

 rows about equal to the plications in width ; about four or five plications 

 originate at the beak, the two lateral ones each giving origin to three or 

 four others from their outer sides, the median ones usually bifurcating 



