LIORHYNCHUS 185 



The species has sometimes been referred to Wilsonia, but it differs from 

 members of that genus in the absence of longitudinal, median grooves 

 upon the plications as they approach the anterior margin. 



Horizon. Salem limestone. 



Genus LIORHYNCHUS Hall 



Description. Shell usually of about medium size, subovate in outline 

 and often subglobular in form. Mesial fold and sinus well developed, the 

 plications obsolete or nearly obsolete upon the lateral slopes of the valves, 

 more or less well developed on the fold and sinus. Internal characters of 

 both valves as in Camarotoechia. 



Remarks. This genus has its greatest development in the Devonian 

 faunas, but a few species are known in the Mississippian. The distin- 

 guishing characteristic of the genus is found in the condition of develop 

 ment of the plications, in combination with the median septum and crural 

 cavity of the rostral portion of the brachial valve. 



LIORHYNCHUS GREENIANUM (Ulrich) 

 Plate XXV, Figs. 27-33 



1886. Rhynchonella greeniana Ulrich, Cont. to Am. Pal., No. 1, p. 26, 



pi. 3, figs, 1-ld. 

 1895. Liorhynchus Greenianus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 



p. 194. 

 1895. Puynax Greenianus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 60, 



tigs. 36-38. 

 1910. Leiorhynchus greeneanum Weller, Bull. Geol. Soe. Am., . vol. 21, 



p. 511, fig. 12. 



Description. Shell of medium size or a little larger, subglobular in 

 form, width usually a little greater than the length, the greatest width 

 near the mid-length of the shell, the postero-lateral margins meeting at the 

 beak in a rounded obtuse angle, the lateral margins rounded, the anterior 

 margin usually broadly emarginate. The dimensions of a nearly complete 

 specimen are : length 28.5 mm. width 28 mm., thickness 24.2 mm. 



Pedicle valve convex in the umbonal region, the surface nearly flat from 

 just in front of the umbo towards the antero-lateral margins in a broadly 

 V-shaped region, from each limb of this V-shaped region the surface 

 curves abruptly to the postero-lateral margins on the outside and more 

 gently into the sinus internally, from the beak to the front along the 

 median line the surface is arched to form nearly a semicircle ; the mesial 

 sinus originating near the middle of the valve as a broad, shallow, gently 

 concave depression which becomes much deeper anteriorly; it is not 

 sharply defined laterally and is produced in front in a broad, lingual ex- 

 tension, rounded in front and usually concave transversely, and -whose 



