556 Systematic Paleontology — Upper Devonian 



to the species at present include forms of small size in the middle and 

 upper horizons of the Chemung it is not certain that such small shells 

 are of the same local type as these here termed var. graciliora. 



Length 25 mm.; width 45 mm. 



This species occurs profusely west of Wills Mountain, rarely east of 

 that locality. 



Occurrence. — Jennings Formation, Chemung Member. National 

 Road west of Frostburg; Oakland- Altamont Road; Oakland-Redhouse 

 Road; Trout Run near Mountain Lake Park; Deer Park; Green Glade 

 Run; Bear Run (Savage River); Allegany Grove, 1750, 2000, 2020 

 abundant, 2050, 2076 abundant, 2111, 2307; EUerslie, Pennsylvania, 1316, 

 1474 common, 1508; National Road on Polish Mountain, 2706 ?; Town 

 Creek, 3584, 3942. 



Collection. — Maryland Geological Survey. 



DOUVILLINA CAYUTA VAR. GRACILIORA n. Var. 



Plate XLIX, Figs. 3-13 



Description. — The prevalent size of this small variety is shown on 

 several crowded slabs where all the individuals are of about the same pro- 

 portions and maintain diminutive dimensions while presenting in their 

 full development the characters of D. cayuta. These shells are more 

 convex than the larger form, the pallial region descending abruptly from 

 about the middle part of the ventral valve, while behind the ridge of this 

 curvature the umbonal region is quite fiat. The surface strife distinctly 

 alternate in size, the cardinal area is fully denticulated and closed except 

 for a very narrow deltidium. Sometimes the shell is extended on the 

 hinge. The small New York expression of D. cayuia has the same 

 characters as those here mentioned but has not been specially studied. It 

 is seldom if ever as abundant as var. graciliora in Maryland. 



Length 9 mm.; width 13 mm. 



Occurrence. — Jennings Formation, Chemung Member. Section on 

 road from Oakland to Altamont; Redhouse abundant; Deer Park; 

 National Road west of Frostburg. 



Collection. — Maryland Geological Survey. 



