202 NEW YORK STATE MUSEUM 



Dimensions. Ventral valves measure in width and length from 40-50 

 to 40-45 mm and dorsal valves about 45 mm in each dimension. 



The size of these shells and their close approach to the contour and 

 details of structure of Hipparionyx leads to easy confusion with the latter. 

 The critical structures of the former are the very conspicuous deeply cleft 

 cardinal process whose lateral walls are continuous with the low crural 

 processes, and also the apparent absence of punctation in the shell. 



Locality. Abundant on Dolbel brook, associated with Hipparionyx 

 proximus; base of Logan's limestone no. 8. 



Rhipidomella logani nov. 



Plate 43, figures- 15, 16, 18, 21 



Prob. Orthis oblata Logan (Billings). Geology of Canada., 1863. p. 393 

 Orthis livia Billings (in part). Palaeozoic Fossils. 1874. v. 2, pt i, p. 32 



Lens-shaped, subcircular shells, subequally convex in the posterior 

 region, the ventral valve depressed anteriorly while the dorsal maintains its 

 convexity. The slope of the surface of the dorsal valve is even in all 

 directions and much more abrupt than in the ventral valve, the former is 

 hence considerably the deeper valve. Little value can be laid upon the- 

 characters of the external markings which in all these species are fine, 

 subequal, rounded and sharply elevated lines. 



In the ventral valve the cardinal area is high and rather narrow, the 

 delthyrium broad and the teeth well defined but not conspicuously elevated. 

 The adductor scar is broad and flabelliform, extending one half the length of 

 the shell and inclosing narrow and elongate oval diductors. The pallial 

 region is well marked by pallial ridges which inosculate freely. In the 

 dorsal valve the cardinal area is narrow and not long enough to materially 

 modify the almost circular outline of the valve. The crural processes are 

 conspicuous and divergent and the cardinal process rather diminutive, 

 curved forward, trifid at its end which does not project beyond the hinge. 



In size, a width of 34 mm and a length of 29 mm is an average 

 maximum and the limit of variation in size is not far from this. 



Locality. In the middle limestones at Grande Greve and Indian 

 Cove. 



Rhipidomella lehuquetiana nov. 



Plate 43, figures 7-13 



Shell small lenticular or subplanoconvex. General outline subcircular, 

 a little wider than long. Ventral valve depressed, beak generally obscured 

 or resorbed, umbo depressed ; a broad and low sinus begins in the umbonal 

 region, widens outward and becomes deep on the anterior margin making 

 a strong sinuosity or tongue extending upward into the other valve. The 



