IS NEW YORK STATE MUSEUM 



LEPTAENA Daluiaii 

 Leptaena rhomboidalis Wilckens. Nacbricht von seltenen Ver- 

 steinerungen. 1769. p. 77 

 Leptaena t e n u i s t r i a t a Hall. Pal. N. Y. 1&47. 1:108 

 Specimens of this lonjj^-lived six^cies were found to occur in the 

 black as well as in the crystalline, gray and compact, reddish 

 limestone pebbles; in the first quite frequently and in large typi- 

 cal specimens, in the latter two in smaller specimens with strong 

 corrugations on the disk, abruptly inflected margin, and the 

 extension of the hinge line forming rather long, acute eaiis. 

 Leptaena rhomboidalis occurs as well in Europe as in 

 America, and ranges here from the Trenton up into the Carbonic. 



(Groups 5, 6, 7) 



PLECTAMBONiTES Pander 



Plectambonites sericeus Sowerby sp. 



Leptaena sericea Sowerby, in Murchison's Silurian 

 system. 1839. pi. 19 



Large typical specimens occur occasionally in the black com- 

 pact limestone pebbles. (Group 5) 



Plectambonites sericeus Sowerby, var. asper James 



Leptaena asper a James. Cin. quar. jour. sci. 1874. 

 1:151 



PI. 1, fig. 6, 7 



A variety with distinct cardinal corrugations was cited by 

 James in his list of the Cincinnati fossils as Leptaena 

 a s p e r a. Later, Meek^ described and figured this variety, stat- 

 ing that it has a large and proportionally wide shell with a 

 straighter anterior margin, and the area of its dorsal valve more 

 inclined forward. A form which shows these characters, with 

 constant strong corrugations, occurs in immense numbers or 

 rather composes the greater number of pebbles of gray limestone 

 at Rysedorph hill, the Moordener kill and Schodack Landing, and 

 is also very common in the matrix at these localities. The cor- 

 rugations are oblique, acute, sharply terminating, large at the 

 cardinal extremities and decreasing in length toward the beak. 

 As the specimens marked characteristically in this manner pre- 



> Pal. Ohio 1873, 1 :T0. 



