THE FOSSIL CRII^OID GENUS DOLATOCRINUS AND ITS ALLIES. 15 



of which may have been movable. Several oi" these slender spines 

 are shown in the figure, and well-defined shallow sockets are seen at 

 the middle of some plates on which the spines are wanting. The 

 plates of the cup are more or less marked by low connecting ridges, 

 which become more j^rominent upward. The cup is a broadly 

 rounded ovoid below, with a tendency to contract a little toward the 

 arm bases. There were apparently 20 arms. Dimensions: Height,. 

 20 mm.; width, 30 mm. Spines occur also on one oi the Maryland 

 species, T. spintilosus, but in the surface characters and form of 

 calyx it is very different from this. 



Horizon and locality. — Niagaran (Bob formation) : Hardin County, 

 Tennessee. 



Type. — Of this and other new species herein described, Frank 

 Springer Collection in United States National Museum. 



Genus STEREOCRINUS Barris. 



The other genus which must be set further back in the time scale 

 is Stereocrinus, hitherto confined to the Middle Devonian, but which 

 now turns up in the Helderbergian as a well marked species, for which 

 I propose the name: 



STEREOCRINUS HELDERBERGENSIS, new species. 



Plate 5, figs. 3, 4. 



In the material obtained by my collectors, Pate and Braun, from 

 the Linden formation at various localities in Benton County, Tennes- 

 see, during a period of several years, were numerous isolated plates 

 of an unknown Camerate crinoid, which by reconstructing a ray 

 from these pieces I identified as Stereocrinus. Afterwards the fortu- 

 nate discovery of a good calyx near HoUiday confirmed the identi- 

 fication. The genus was founded upon specimens from the Hamilton 

 of northern Michigan, and so far as I know it has not been recognized 

 in the Onondaga beds of the Louisville area. In the Michigan form 

 the calyx is strongly lobed in the zone of the arm bases, whereas in 

 the present species there is no interradial depression whatever, and 

 the arm bases form an almost continuous ring. Similar differences 

 occur between species of Dolatocrinus. The plates of the cup in this 

 species as found are usually smooth, with a low median ridge on the 

 radial series, but when well preserved are marked by a sharp and fine 

 striation. The tegmen is evenly convex, appearing too high in the 

 figured specimen on account of pinching, and is composed of smooth 

 plates. The specimen illustrated measures 30 mm. high and 42 mm. 

 in diameter. Isolated plates indicate that a larger size was attained. 



There is also fragmentary evidence of the existence of a large 

 species of Dolatocrinus in the same beds with the Stereocrinus. 



Horizon and locality. — Helderbergian (Linden formation) : Benton 

 County, Tennessee. 



