Maryland Geological Survey 647 



Occurrence. — Jennings Formation, Chemung Member. Allegany 

 Grove, 2GG2 ; Williams Eoad, on Polish 3Inunhun. 2^S-i ; Town Creek, 

 2238 common, 2391, 2496 ?, 3593, 4631 ; near Pennsylvania-Maryland 

 state line, west of Tonoloway Ridge near school house in lower conglom- 

 erate zone. Millstone, 2322, 3116 abundant. A smaller form, probably 

 of this species, occurs at Town Creek, 3760, 3870. Parkhead Member. 

 Two miles west of Pawpaw, West Virginia, IIGS; Millstone, 1772 

 abundant. 



Collection. — Maryland Geological Survey. 



SCHIZODUS frostbergensis n. sp. 

 Plate LXIV, Fig. 15 



Description.-^Shell small, elliptical-ovate, length about 1.4 times 

 height; hinge-line short. Anterior margin rounded; posterior margin 

 oblique, nearly straight above, abruptly rounded at junction with ventral 

 margin ; ventral margin curved. Beaks situated about one-third length 

 of shell from anterior extremity, small, slightly elevated above hinge-line, 

 incurved. Valves convex, somewhat gibbous beneath umbo; surface slop- 

 ing regularly towards margins; umbonal slope not angular, indistinct. 

 Anterior and posterior muscular scars distinct. Surface not distinctly 

 observed, probably smooth. 



Length 14 mm.; height 10 mm. 



This species is quite distinct from previously described species of this 

 genus in its general expression. 



Occurrence. — Jennings Formation, Chemung Member. Town 

 Creek, 3760, 3870. 



Collection. — Maryland Geological Survey. 



SCHIZODUS TRIGONALIS n. sp. 



Plate LXIV, Figs. 16-18 



Description. — Shell large, triangular to rhomboidal; equivalve; slightly 

 longer than high; hinge-line short. Anterior and posterior margins 

 slightly curved, oblique; ventral margin curving strongly at its junction 



