Maryland Geological Survey 553 



dorsal valve the cardinal process is strong and deeply bifurcate, sup- 

 ported by thick divergent and papillose ridges which bound the obscurely 

 defined muscle impressions. These shells attain considerable dimensions, 

 are frequently extended on the hinge-lino, and show no internal characters 

 which are not normal to the species itself. 



The species Leptostrophia perplana is one of the flat stropheodontids 

 that makes its appearance early in the Devonian, becoming quite abundant 

 in the Hamilton stage and also occurring with normal characters in the 

 Chemung of New York. 



Length 30-35 mm.; width 35-40 mm. 



Occurrence. — Jennings Formation, Chemung Member. National 

 Eoad west of Tonoloway Kidge. This shell seems not to be widely dis- 

 tributed but has been found abundantly in the vicinity of Oakland, 

 Cherry Creek, near Mitchell House on Altamont Eoad and Deer Park, 

 Garret County. 



Collection. — Maryland Geological Survey. 



Leptostrophia perplana var. alternata n. var. 

 Plate XLVIII, Figs. 5, 6 



Description. — This variety resembles L. perplana var. nervosa in having 

 nodose striae and in its muscular scars. It differs from that variety in 

 having alternating coarse and fine strife and is frequently smaller than 

 the usiTal size of var. nervosa. It resembles L. interstrialis in possessing 

 alternating coarse and fine stride but differs in the more strongly nodose 

 character of the striae. It seems to be a transitional form connecting 

 these two species. 



Length 11 mm. ; width 16 mm. 



Occurrence. — Jennings Formation, Chemung Member. Section on 

 National Eoad west of Frostburg; Trout Eun near Mountain Lake Park; 

 Williams Eoad on Polish Mountain, 2042 abundant; Town Creek, 2122, 

 2391 abundant. 



Collection. — Maryland Geological Survey. 



