296 New Species of Crinoidea from the 



angles, between which the sub-radial plates rest. Sub- 

 radials large, obtusely angular above and below, four 

 hexagonal and one heptagonal. First radial plates sub- 

 pentangular, a little wider than high, strongly indented 

 above, marked by a rnedium-sized, elevated, sub-central 

 scar for the attachment of the arm plates. Anal plates 

 and arms unknown. Column large, round, composed 

 near the body of very thin equal plates. Surface of plates 

 marked by strong elevations and depressions, forming a 

 series of ridges which originate from the basal plates, bi- 

 furcate on the sub-radials, and reunite below the scar 

 of the first radial plates ; a second set of less strong 

 ridges unites the sub-radials across their lateral margins ; a 

 third and the strongest series of ridges unites the first ra- 

 dials across their lateral margins. 



These ridges are formed by the bending or folding of the 

 plates, which are thin, and afford very little substance for 

 their attachment to each other ; and this is probably the 

 reason that there are seldom any but detached plates of 

 this species found, while, from their frequency, it must 

 have been a comparatively abundant species. 



This species is closely related to C. rhombiferus and 

 C. sculptilis in form ; but the strong ridges and otherwise 

 smooth surface, with its comparatively small articulating 

 scar, distinguish it. The column is also much larger 

 than in those species. The separated plates are strong- 

 ly undulated upon the sides, with a sinuous margin. 

 These deep sinuosities of the plates of very old specimens 

 show spiculae or bars of calcareous matter extending across 

 the cavity from side to side, thus strengthening the thin 

 joining faces of the plates. 



Geolog-ical formation and locality. Burlington lime- 

 stone, Burlington, Iowa. Collections of Rev. W. H. Bar- 

 ris, C. A. White, and Br. O. Thieme. 



Cyathocrinus incipiens (n. s.). Calyx extremely small. 



