TRENTON CONGLOMERATE OF RYSEDORPH HILL 87 



does not show any difference from the Cincinnati type, nor any 

 approach to the other, partly larger Trenton species, described 

 by Ulrich. One specimen has been figured to show the remark- 

 able tumidity of the central ventral third, which may be caused 

 by a state of pregnancy, such as is frequently indicated in 

 valves of Beyrichias. (Groups 5, 6, 7) 



LEPiDocoLEus Fabcr 



Lepidocoleus jamesi Hall & Whitfield sp. 



Plumulites jamesi Hall & Whitfield. Ohio geol. sur. 

 Pal. 1875. V. 2, pt 2, p. 106 



PI. 4, fig. 16-19 

 The black limestone of the Rysedorph hill conglomerate fur- 

 nished two plates with crustacean structure, which, on compari- 

 son, proved identical with a specimen collected in the Eiafines- 

 quina deltoidea bed of the upper Trenton limestone of Trenton 

 Falls. The latter has been figured by the writer in another 

 paper, for comparison with the figures of specimens of Lepi- 

 docoleus jamesi, found to occur profusely in the lower 

 Utica beds of Mechanicsville, and occasionally in the upper 

 Utica beds on Oreen Island. Hall and Whitfield remark 

 that they detected fragments apparently identical with their 

 Plumulites jamesi on surfaces of Trenton limestone 

 from Trenton Falls, and the writer in a former paper concurred 

 with this identification, and is as yet not prepared to separate 

 thel Trenton and the later formis, though it seems that the 

 Trenton specimens have more closely arranged transverse stri- 

 ations. A critical comparison of the Trenton and Utica mate- 

 rial is however greatly hindered by the very different preserva- 

 tion of the plates in the shale, where they are nearly completely 

 flattened and reduced to a mere film, and in the limestone, where 

 they retain all details of profile and surface sculpture. The 

 latter fact makes the specimens from Rysedorph hill specially 

 worthy of notice. This surface sculpture consists of a very 

 delicate but distinct cross striation of the interspaces between 

 the coarser transverse striations, consisting of two systems of 



