46 H. 8. Williams — Crustacean from the Devonian. 



garded by him as the equivalent of the third oil saud of the 

 Venango oil district of that State. In the same stratum and 

 above it are t} 7 pical Chemung fossils. 



It occurs just at the junction between the sandstone and a 

 stratum of soft, fine argillaceous shale, and, in the process of 

 weathering, the fine shale has been washed away, leaving a 

 sharply defined cast of the fossil in hard sandstone, though no 

 portion of the original crust is preserved. 



The associated species are Spirifera Verneuilii Murch. (=Sp. 

 disjuncta Sow.), and Rhynchonella contracta Hall ; and in the 

 shales just above the sandstone occur Chonetes scitula Hall, 

 " Chonetes " muricata Hall, an Ambocoelia uinbonata Hall, a 

 small Productus of the type of Hall's Productella Boydii, the 

 coarse ribbed Orthis Leonensis Hall, and a Rhynchonella agree- 

 ing with some of the wider forms of R. sappho Hall. 



The fauna is the characteristic Upper Chemung fauna of 

 western New York and adjacent area. In this area some of 

 the species occur among the earliest Chemung species; no 

 characteristic Carboniferous types have been detected. The 

 fauna may be considered, therefore, as a pure Devonian fauna. 



The general form and structure of the specimen place it 

 among the Merostomata with anchylosed thoracico-abdominal 

 segments, but as only the under side is exhibited, its identifi- 

 cation with Presiwichia must be regarded as provisional, since 

 we are ignorant of the structure of the under surface of authen- 

 tic members of that genus. 



I propose as a name for it, 



Prestwichia Eriensis, sp. n. 



The following characters exhibited by the specimen are 

 regarded as generic and as locating it in the genus rrestwichia 

 of Woodward: (1), the elliptical head shield; (2), the genal 

 spines which proceed backward more directly than in any 

 described species of the genus ; (3), the thoracico-abdominal 

 segments anchylosed to form a buckler, to which is attached 

 (4) a long telson. The general outline of the whole animal 

 resembles that of the modern Limulus. 



The evidence of a solid thoracico-abdominal buckler is found 

 in the continuous surface across the body, from which proceed 

 four (visible) short marginal spines each side the telson, and 

 upon which are seen at least eight narrow ridges running lon- 

 gitudinally to near the margin. 



The remaining characters may be, in part, of generic value, 

 but they constitute the distinctive characters of the species, as 

 far as these can be made out from the specimen. 



The under side of the body presents three well defined 

 tracts, viz: (AB), the cephalic shield which is evenly rounded 

 in front and is laterally prolonged backward into two genal 



