EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 113 



the Presque Isle outcrops the large and thickened hinge plate is fully devel- 

 oped and was completely perforated at maturity. Likewise the strong 

 adductor muscle scars separated vertically by a low septal ridge have quite 

 the expression they display in fully developed specimens of R . ovoi des 

 and they even show the peculiar divergent vascular markings over the pos- 

 terior slopes which have been heretofore recorded only in a single example 

 of R. ovoicles [Palaeontology of N. Y. v. 8, pt 2, pi. 75, fig. 5]. 



These are structural features important to emphasize, for no other 

 species thus far described reproduces these details of that well known 

 Oriskany shell so well. In the ventral valve, also, mature shells bear the 

 expression of R . o v o i d e s in their fully developed dental lamellae and 

 deep pedicle pit. The shells of this species in early stages are transverse 

 or subcircular rather than elongate, the increase of length being an acquisi- 

 tion of later growth. The hinge line is straight and extends for the full 

 diameter of the shell giving the latter a semicircular outline. 



On both ventral and dorsal valves a distinct and prominent cardinal 

 area is present. The straight hinge line extending for nearly the entire 

 width of the valve makes this a conspicuous feature, on the dorsal valve the 

 area maintaining its notable width to the extremity of the cardinal line and 

 then quickly losing it on the hinge angles. In the ventral valve this feature 

 is made more prominent by the greater elevation of the beak and consequent 

 greater width of the area. 



To a certain degree this structure is comparable to that observed in the 

 subgenus Beachia H. & C. (type, R. suessana Hall, Oriskany, Cum- 

 berland, Mel.). In this shell "the cardinal margin beneath the beak [of the 

 ventral valve] is flattened into a well defined pseudoarea" [Pal. N. Y. v. 8, 

 pt 2, p.25gj. Here, however, is a high development of a cardinal area to a 

 degree far beyond that expressed in Beachia. Furthermore in Beachia 

 "the short inflection of the margin beginning here [on the hinge line] is 

 continued along the lateral portion of the shell where it meets a similar 

 marginal inflection from the opposite valve. These produce the sharp 

 introversion of the lateral margins which is also one of the characteristics 

 of the genus Megalanteris." No such reentrant margins occur in the shells 

 under consideration. I would not refer the species to the subgenus Beachia 

 lest thereby its real affinities be obscured. 



The kindness of Prof. E. Kayser of Marburg has enabled me to com- 

 pare my material with typical examples of the Rensselaerias, R. strigi- 

 ceps F. Roemer and R. crassicosta (Koch) Kayser, of the lowest 

 arenaceous Devonic of the Rhine, and my lamented friend, the late Dr L. 

 Beushausen of the Landesanstalt, Berlin, compared some specimens from 

 the Presque Isle stream fauna with examples of the species mentioned, in 

 the collections of that institution. 



The evidence at hand is very clear that while the specimens currently 



