240 THE DEVONIAN OF MISSOURI. 



little elevated above the opposite. A cast of the interior shows a broad shallow de- 

 pression extending half way to the anterior margin. 



Brachial valve larger than the pedicle, and strongly convex to gibbous. Near the 

 anterior margin it is elevated into a broad, sharply defined fold. At the lateral margins 

 the shell becomes abruptly inflected, forming a flat area corresponding to a similar one 

 on the other valve. 



Surface of each valve marked with about 40 angular plications, the last two or 

 three near the hinge becoming almost obsolete. Ten of the plications occupy the sinus, 

 fndistinct concentric lines of growth are present. 



Remarks — Two specimens referable to this species have been observed, one a nearly 

 complete individual, the other a cast of the interior of the pedicle valve. 



Horizon — Lower beds. 



Holotype and Allotype No. 27464 Walker Museum. 



Uncinulus welleri sp. no v. 

 Plate 63, figures 13-14. 



Description — Shell of medium size, elongate oval, sub-pentagonal in outline. The 

 dimensions of the holotype are: Length 30 mm., width 27 mm. Some specimens are 

 larger, as much as 35 mm. in length, and 30 mm. in width. Shell characterized by 

 flat and serrated lateral margins, and by gently concave postero-lateral margins which 

 slope steeply to the beak. 



Pedicle valve arched in the umbonal region, becoming strictly concave toward 

 the anterior margin and forming a broad shallow sinus which becomes extended into a 

 linguiform projection. Lateral margins inflected, forming flat lateral areas. Beak 

 small, and incurved closely over that of the opposite valve. 



Brachial valve highly convex, the anterior margin elevated into a scarcely percep- 

 tible fold. Toward the lateral margins the shell surface slopes abruptly, forming con- 

 tinuous flat areas with those produced by the inflection of the opposite valve. Beak 

 sharply pointed, incurved below the other. 



Surface of both valves marked with 40 to 50 simple angular plications, which are 

 separated by deep, narrow furrows. Seven plications occupy the sinus. 



Remarks— Only a few examples of this species have been observed. It may be dis- 

 tinguished from Uncinulus salinensis by its more elongate form, and by the less promi- 

 nent fold and sinus. The species resembles Uncinulus nobilis Hall from the Helder- 

 bergian of New York, and may be a later development of that form, but it differs in 

 being larger, in having a greater number of plications, and a flatter and less sharply 

 marked mesial sinus. 



Horizon — -Lower beds. 



Holotype and Paratype No. 27465 Walker Museum. 



Name — This fossil has been named after Professor Stuart Weller, of the Depart- 

 ment of Paleontology, University of Chicago. 



Genus Plethorhyncha Hall and Clarke 



Plethorhyncha barrandii (Hall) 

 Plate 63, figures 15-16. 



1857. Rhynchonella barratidii Hall, Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., 



p. 82, figs. 1-3; pi. 84, fig. 4. 

 1908. Plethoryncha barrandii Clarke, Mem. M. Y. State Mus., vol. 9, pt. 1, p. 171, 



pi. 28, figs. 16-17. 

 1913. Camarotoechia (Plethoryncha) barrandti Schuchert, Geol. Surv., Md. Low. Dev., 



p. 359, pi. 64, figs. 2-3. 



