42 NEW YORK STATE MUSEUM 



Dalmanella cf. hybrida Sowerby (sp.) 



Plate 4, fig. 7, 8 



Orthis hybrida Sowerby, in Murchison's Silurian System. 1839. p. 630, pi. 13, 



fig. n 

 Orthis hybrida Hall, Paleontology of New York. 1852. 2: 253, pi. 52, fig. 4a-c ; 



and authors generally 



A single depauperated ventral valve with the characters of this species 

 has been observed in the chert nodules at Rochester. Orthis hybrida 

 is found at various outcrops of the Racine beds of Wisconsin, but has not 

 been elsewhere identified in typical Guelph rocks. 



leftaena Dalman. 1828 

 Leptaena rhomboidalis Wilckens 

 For synonymy see Schuchert, United States Geol. Sur. Bui. 87, p. 240 

 Under the name L. depress a, Hall ' reports this species as com- 

 mon in the Rochester shale and rare in the Lockport limestone. A single 

 small specimen has been obtained from the lower Shelby dolomite. As this 

 cosmopolitan shell is not mentioned from the Guelph of Canada or Ohio, in 

 Wisconsin has been reported only from one locality of that formation, and 

 is entirely absent from the upper horizon at Shelby and Rochester, it evi- 

 dently found very uncongenial conditions in the Guelph basin. 



spirifer Sowerby. 181 5 

 Spirifer crispus (Hisinger) Hall 



Plate 4, fig. 10-20 



Spirifer crispus Hall, Paleontology of New York. 1852. 2 : 328, pi. 74, fig. oa-h 

 The Spirifers occurring in the upper Shelby horizon both at Rochester 

 and Oak Orchard creek present features of considerable interest and signifi- 

 cance. They naturally fall into two groups, one of small and broad forms, 

 of which numerous specimens have been observed, the other of larger and 

 relatively longer form, occurring in but restricted number. 



The smaller of these is identical in expression with the S p. cris- 

 pus described by Hall from the Coralline (Cobleskill) limestone. All the 



'Pal. N. Y. 2:258. 



