TRENTON CONGLOMERATE OF RYSEDORPH HILL 15 



Dimensions. Length 3.9 mm, width 3.7 mm, hight 4 mm. 



Horizon and locality. Black compact limestone pebble of con- 

 glomerate of Rysedorph hill. 



Observations. In common with the only other pedicle valve of 

 Siphonatreta m-innesotensi s known, this form has 

 the depressed median region and the concentric wrinkles, while it 

 differs in size and the relative length of the spines, the latter 

 being much larger in the New York specimen. The importance 

 of this difference can, with only the two pedicle valves known 

 thus far, not be properly adjudged. 



The interesting feature of the specimen from Rysedorph hill 

 is that it shows distinctly the elevated conic beak with perfo- 

 rated apex, a feature distinctive of the genus Siphonotreta, as 

 restricted and more properly defined by Hall and Clarke. 1 As 

 remarked before, the other American specimens tentatively 

 referred to this genus have not furnished sufficient data for 

 their generic determination. The specimen from Rysedorph hill 

 indicates that Siphonotreta minnesotensis is the 

 first undoubted American representative of that peculiar, 

 eminently lower Siluric genus, which is well represented in 

 Europe and extends with but one species into the upper Siluric. 



(Group 5) 



crania Retzius 



Crania cf. trentonensis Hall. Descriptions new species Crinoidea 



and other fossils. 1866. p. 12 



In the black compact limestone of Rysedorph hill a small 



internal cast of a Crania was found, showing two deep divergent 



oval central muscle pits on the apex and a third shallow one 



below. As the internal parts of the Trenton species of Crania 



are not jet known, a closer comparison is not possible. 



pholidops Hall 



Pholidops trentonensis Hall. N. Y. state cab. nat. hist. 24th an. 



rep't. 1872. p. 221 



A single but finely preserved specimen with regular oval out- 

 line and strong lamellose growth lines was found in the compact 



1 Pal. N. Y. 1892. v. 8, pt 1, p. 177. 



