Mauylaxd Geological Survey 627 



ilton of New York but the concentric strije wliicli omamcnt the surface 

 of that species have not been observed, as casts of interior only liave been 

 foi;nd in Maryland. 



Occurrence. — Jennings Formation, Chemung Member. Allegany 

 Grove, 1633 ; Town Creek, 3760, 3870. Parkiiead Member. Four miles 

 southeast of Pratt on White Sulphur Branch. 



Collection. — Maryland Geological Sun-ey. 



Superfamily ARCACEA 

 Family PARALLELODONTIDAE 



Genus MACRODON Lycett 



Macrodon chemungensis Hall 



Plate LXI, Fig. 18 



Macrodoyi chemungensis Hall, 1870, Prelim. Notice Lammellibr., pt. ii, 



p. 14. 

 Macrodon chemungensis Hall, 18S5, Pal. of N. Y., vol. vi, pt. i, sec. ii, p. 350, 



pi. Ii, figs. 11-16. 



Description. — " Shell of medium size or larger, arca^form ; cardinal 

 and basal margins subparallel; length more or less than twice tlie height; 

 basal margin nearly straight or gently curving with a slight constriction 

 anterior to the middle. Posterior end broad, subtruncate or sometimes 

 rounded. Cardinal margin straight, extremities angular. Anterior end 

 rounded below, tnmcate above. Valves convex in the posterior portion., 

 becoming gibbous in the middle and anterior. Beaks subanterior, prom- 

 inent, rising a little above the hinge-line. Umbonal region gibbous, with 

 a prominent, undefined ridge extending toward the postinferior extrem- 

 ity, and a vertical depression extending from the umbo to the base. Sur- 

 face marked by irregular, concentric, lamellose lines of growth. Three 

 specimens measure respectively 31, 27, and 23 mm. in length, and 14, 15, 

 and 10 mm. in height. This species is distinguished by its parallel basal 

 and cardinal margins, the truncated posterior end and its narrow form." 

 Hall, 1885. 



A single valve has been observed which seems clearly referable to the 

 species. 



