Makylaxd Gkoi.ooical Suuvey 581 



Genus LIORHYNCHUS Hall 

 LlOEHYNCHUS MESACOSTALE Hall 



riate LIV, Figs. 5-S 



Atrypa viesacostalis Hall, 1843, Geol. of N. Y., Rept. on the 4th Dist., p. (;4, 



figs, a, b. 

 Leiorhynchus mesacostalis Hall, 1SG7, Pal. of N. Y., vol. iv, p. 3U2, pi. Ivii, 



figs. 18-2.5. 



Description. — Shell of rliTnclionelloid aspect with but moderately con- 

 vex valves and quite low median fold and sinus. Fold and sinus hear three 

 or four rounded plications whicli ilo not reach the heak, while on the 

 lateral slopes of the valves plications arc obscure or altogether obsolete 

 leaving the surface smooth. With good preservation the exterior shows 

 fine concentric lines crossed on the lateral slopes by radial striae. In 

 the dorsal valve a low median septum reaches to about the middle of the 

 shell and at the l)eak supports a small triangular spondyliuni. In the 

 ventral valve the muscular scars are almost linear and situated posteriorly. 

 This species is common in the Ithaca fauna and in the overlying Chemung 

 beds of southern central New York. 



Length 18 mm.; width 20 mm. 



Occurrence. — Jennings Formation, Pakkiiead Member. Allegany 

 Grove, 850 abundant; 214 miles southeast of Cumberland, south of Poto- 

 mac Eiver; Williams Road, east of Cumberland, 1393 abundant. 



Collection. — Maryland Geological Survey. 



LlORHYNCHUS cf. MULTICOSTUM Hall 



Plate LIV, Fig. 9 



LeiorhyncJius multicosta Hall, 1860, loth Ann. Rept. N. Y. State Cab. Nat. 



Hist., p. 85. 

 Leiorhynchus multicosta Hall, 1867, Pal. of N. Y., vol. iv, p. 358, pi. Ivi, 



figs. 26-40. 



Dcscriiiiion. — Shell ovate in outline; biconvex; ventral valve oibbous 

 on the umbo, depressed medially to a broad sinus. Dorsal valve the more 

 convex with a broad median fold. Surface marked by rounded or sub- 

 angular plications of which usually 3 to 6 are in the sinus and on the 

 fold and 5-8 on each lateral slope. Fine concentric lines cover these ribs. 



