384 Systematic Paleontology 



Young specimens of E. marylandica, before the inflection is much de- 

 veloped, resemble R. svhglohosa and in this points to its ancestry. If the 

 individual is of the elongate type the inflection may become very decided, 

 developing into the typical form of E. marylandica. When the shell is 

 shouldered posteriorly inflection is never so greatly developed and the 

 individual remains smaller than the typical form. This form, before 

 inflection develops, Hall named E. intermedia, but it seems to have no 

 stratigraphic nor geographic significance ; and the name can therefore be 

 dropped. 



Average length about 3.75 cm. ; width about 2.5 cm. 



This species is abundant at most localities. A few places only are 

 named in the following paragraph : 



Occurrence. — Oriskany Formation, Eidgely Member. Cumberland, 

 Hancock, Maryland; Warren Point, Pennsylvania, where it attains a 

 length of 95 mm. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



RENSSELiERIA MARYLANDICA VAR. SYMMETRICA n. var. 



Plate LXVI, Fig. 25 



Description . — "Retaininj? juvenile characters throughout life (those of 

 E. subglohosa) and attaining the largest growth of Maryland Rensse- 

 Iserias. It is further distinguished by having the greatest width in the 

 anterior region. 



Length 4.5 cm. ; width 3.4 cm. 



Occurrence. — Oriskany Formation, Ridgely Member. Cumberland. 



Collection. — Maryland Geological Survey. 



Renssel^ria keyserensis n. sp. 



Plate LXVI, Figs. 26-28 



Description. — Shell oval, biconvex, length and width subequal. Ventral 

 valve gibbous, point of greatest convexity posterior to middle. Umbo 

 elevated, extending a little beyond that of dorsal valve over which it is 

 incurved. Shell flattened in middle or having a very shallow mesial sinus 



