158 C. D. WALCOTT — DISCOVERY OF SILURIAN VERTEBRATES. 



-hales the water deepened, the iehthyic fauna disappeared, and the typical 

 invertebrate fauna of the Trenton epoch of New York nourished and was 

 imbedded in the calcareous sediments. The study thus far made of the 

 upper portion of the Silurian (Ordovician) section and the Carboniferous 

 strata has not shown the presence of Silurian or Devonian strata. If 

 deposited in this region they were eroded away by the Carboniferous sea. 

 The study of the breccias resting on the Carboniferous, or forming its 

 upper portion, may possibly throw some light upon this interval. Mr. 

 Stanton considers that the detailed sections give evidence of at least two, 

 and perhaps three, periods of upheaval and erosion from the Silurian 

 (Ordovician) to the Trias, inclusive. 



The Invertebrate Fauna. 



Harding Sandstone. — The invertebrate fauna of the sandstone series is 

 molluscan with the exception of one species of crustacean. As would be 

 expected in such a deposit, the acephalus mollusks number more than 

 onedialf of the species of the entire fauna. The largest number of speci- 

 mens were collected in h and rf of the section, figure 1. The fauna has 

 been partially identified and will be more thoroughly studied when the 

 collections now being made are available. The genera and species 

 recognized are as follows : 



BRA< JHIOPODA. 

 Lingula, like /.. attenuata, Salter, and L. belli, Billings. 



/. . 1 MELLIBRA NCHIA TA . 



Modiobpsis, like M. trentonensis. Cypricardites,2 sp. undet. 



" •". sp. undet. Orthonota, sp. undet. 



< ypricardites, like C. ventricosa, Hall. Tettinomya, 3 sp. undet. 

 like C. rotundata, Hall. 



GASTEROPODA. 



Helicotoma, >\>. undet. Murchisonia, sp. undet. 



Pleurotomaria, sp. undet. 



CEPHALOPODA. 



Orthoceras multicameratum, Hall. Oytoceras, sp. undet. 



( RUSTACEA. 

 Leperditia, type of L.fabidites, Conrad. 



