176 Systematic Paleoxtology — Middle Devoniax 



Leiorhymhus Hmitaris Hall, 1867, Pal. N. Y., vol. iv, p. 356, pi. Ivi, flgs. 6-21. 

 Liorhynchits limitnris Hall and Clarke, 1893, Pal. N. Y., vol. viii, pt. ii, p. 194, 



pi. lix, flgs. 1-5. 

 Leiorhynchus Umitare Schuchert, 1897, Bull. U. S. Geol. Surv., No. 87, p. 237. 

 Liorhynchus Umitare Clarke, 1903, N. Y. State Mus., Bull. 65, p. 253. 

 Leiorhynchus Umitare Grabau and Shinier, 1909, N. Am. Index Fossils, vol. i, 



p. 289, figs. 357a, b. 



Description. — Shell ovate, suborbicular or transverse; moderately or 

 extremely gibbous, except in tbin sbales, where it is almovst flat; sinus 

 and mesial fold more or less developed. Ventral valve in young shells 

 scarcely less convex than the opposite, becoming gradually more dis- 

 similar with growth; in old shells it is rather gibbous near the beak, 

 gradually depressed below, becoming deeply sinuate, produced in front 

 and abruptly tmncate. Dorsal valve more convex than ventral, gibbous 

 in old shells, the mesial fold becoming developed below the middle of its 

 length ; umbo gibbous and often rising nearly as high as the beak of the 

 ventral valve. Surface marked by numerous angular or subangular pli- 

 cations, those of the mesial fold and sinus distinctly bifurcating, while 

 sometimes a few of those on the sides are divided; concentrically marked 

 by fine striae. 



Tn the fissile black shales, forming the lower part of the Eomney 

 formation in Maryland (the best locality noted is the southern end of the 

 B. & 0. E.. E. cut at 21st Bridge), specimens are common of a nearly flat 

 LiorJii/nchns, the fonn of which is due to crushing, wliich are referred to 

 this species. The outline is similar to tliat of the young specimen of L. 

 multicosta = laura represented by fig. 26 on pi. Ivi, vol. iv, Palaeontology 

 of New York; but none of these specimens reach the size of the adult of 

 that species, the plications are somewhat finer, and those of the mesial 

 fold and sinus distinctly bifurcate. Whik' the specimens do not agree in 

 I'urm with those from the calcareous^ layers of the ]\Iarcellus sbales, they 

 are similar to the flattened specimen from " tliinly laminated shales" 

 represented by fig. 21 of the above-mentioned plate, and also similar in 

 general appearance to specimens of this species which the writer has col- 

 lected in the thin black shales of the Xew York Marcellus. Tlie Mary- 

 hind sjxH'inieiis show no appreciahh' ditl'crences from flattened speci- 



