Notices of Memoirs — U. S. WilUams — On a Fossil Limulus. 427 

 j^OTioiBS OIF nvniEivrioiS/S. 



Notice of a new Limuloid Crustacean from the Devonian.'' 

 By Henry Shaler Williams, of the Cornell University. 



AMONG the fossils collected last summer for a comparative study 

 of the Devonian faunas, an interesting form was discovered in 

 Erie County, Pennsylvania, worthy of special notice. 



The specimen was found in a bluish sandstone (which in places is 

 a fine pebbly conglomerate) at Le Boeuf called the " 3d oil-sand," by 

 Mr. I. C. White, in the Keport Q 4 of the Second Geological Survey 

 of Pennsylvania (p. 239), and regarded by him as the equivalent of 

 the third oil-sand of the Yenango oil-district of that State. In the 

 same stratum and above it are typical 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. 

 disjmicta, Sow.), Bhyiichonella contracta, Hall ; and in the shales just 

 above the sandstone occur Chonetes scitula, Hall, " Chonetes " muricata, 

 Hall, an Ambocoelia umbonata, Hall, a small Productus of the type 

 of Hall's Productella Boydii, the coarse ribbed Ortliis Leonensis, Hall, 

 and a Bhynchonella agreeing with some of the wider forms of B. 

 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 identification with Prestwichia 

 must be regarded as provisional, since we are ignorant of the struc- 

 ture of the under surface of authentic members of that genus. 



I propose as a name for it, Prestwichia Eriensis, sp. nov. 



The following characters exhibited by the specimen are regarded 

 as generic and as locating it in the genus Prestwichia 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 Litnulus. 



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 longitudinally to near 

 the margin. 



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

 ^ Sillimaa's American Journ. of Sci. vol. xxx. July, 1885, p. 46. 



