Maryland Geological Suhvet 593 



" Dorsal valve depressed or moderately convex, with a wide and usually 

 undefined mesial fold which is much expanded below, leaving the anterior 

 margin sinuate; sides of the shell somewhat regularly curving, and a 

 little flattened at the cardinal extremities. 



" Surface usually smooth, or marked only by concentric lines of growth. 

 In older shells there are sometimes a few obscure and undefined radiating 

 folds. 



" The interior of the ventral valve shows strong short teeth with the 

 dental lamellae much thickened, filling up the rostral cavity and extending 

 along the sides of the upper part of the muscular impression ; the muscu- 

 lar space is of small or of moderate size, deeply marked, and often pre- 

 serving a distinct median crest. 



" In the dorsal valve the muscular impression is small and narrow, and 

 usually not deeply marked. The cardinal process is strongly striated, 

 and this character is distinctly preserved in the cast." Hall, 1867. 



Length. 20 mm.; width 28 mm. 



The occurrence of this species in Maryland is of much interest since 

 it is one of the most important members of the Ithaca fauna of Ne^v 

 York where it is restricted to two horizons, one near the base and a 

 second near the top of the beds containing that fauna. 



Occurrence. — Jennings Formation, Woodjioxt Member, Ithaca 

 Fauna. Hancock, 690 abundant, 935; Berkeley Springs, West Virginia, 

 712 abundant, 755. 



Collection. — Maryland Geological Survey. 



Genus SPIRIFER Sowerby 



Spirifer disjdnctus Sowerby ' 



Plate LVI, Figs. 7-14 ; Plate LVII, Fig. 1 



Spirifer disjunctus Sowerby, 1840, and Sp. verneuili Murchison, 1840, and 

 of authors generally. 



Description. — Among Devonian Spirifers no species is better known or 

 so widely distributed as this. Throughout the world wherever later 



^ For extended synonymy and illustrations of American forms see Pal. of 

 N. Y., 1867, vol. iv, p. 243, pis. xli, xlii; also Pal. of N. Y., 1894, vol. viii, pt. ii, pi. 

 XXX, figs. 14-17. 

 38 



