556 



NORTH AMERICAN INDEX FOSSILS. 



(Fig. 1888.) Siluric. 



172. M. roemeri Wachsmuth and Springer. 

 Plates smooth. 



Upper Niagaran (associated with Astrcuospongia meniscus) of 

 Tennessee. 



173. M. nobilissimus (Hall). Siluric ?-Devonic. 

 Larger than M. pachydactylus, with longer dorsal cup and with 



nearly straight sides. Interradial spaces more deeply impressed 



above. Radiating ridges 

 less conspicuous and with- 

 out nodes. Arms and pin- 

 nules more crowded in that 

 species. 



Niagaran (?) of Ten- 

 nessee ; Helderbergian of 

 New York. 



174. M.bainbridgensisHall 

 and Whitfield. De- 

 vonic. 



Dorsal cup rapidly 

 spreading, with convex 

 sides. Plates covered with 

 granules. Suture lines 

 grooved. 



Hamilton of New York 

 and Ohio. 



175. M. pachydactylus 

 (Conrad). (Fig. 

 1889.) Devonic. 



Radiating ridges conspicuous and ending in a node at center 

 of plates. 



Helderbergian of New York. 



LXVI. DoLATOCRiNUS Lyon. 

 Calyx depressed. Dorsal cup flattened below, sometimes to the 

 full height of the costals. B anchylosed, with lines of union 

 obliterated. R large and 6-sided. Costals two. Interbrachials 

 usually in three ranges, the first consisting of one plate (the largest 

 of the calyx) and followed by a second row of one plate. Narrow 

 slits present between the interambulacral plates, four to six in 



Fig. 1889. 



Melocrinus pachydactylus. 

 Hall. ) 



(After 



