THYSANOCRINID^. 201 



radial dome plates spinous; the anus excentric and at the top of a large 

 protuberance. 



Distribution, — So far as known, restricted to the Niagara group of 

 Indiana. 



RemarTcs. — The genus has its closest relations with ThysanocrinuSy from 

 which it differs in the depressed form of the calyx, the pendent arms, and 

 in the spine-bearing disk. 



Hyptiocrinus typus W. and Sp. (nov. spec). 

 Plate XIX, Figs. 6a to c. 



1892. W. and Sp. ; Am. Geologist, Yol. X. (September), p. 138. 



Syn. Cyphocrinus Qorbyi S. A. Miller (October 26, 1892). Adv. Sheets IStli Eep. Geol. Surv. 

 Indiana, p. 51, Plate 7, Tigs. 14, 15, 16. 



Specimens of medium size. Calyx wheel-shaped, nearly once and a half 

 as wide as high. Dorsal cup broadly obconical to the top of the costals, then 

 flanging outward and somewhat downward. Arm regions not lobed, but the 

 upper margins of the interbrachial and interdistichal spaces formed into 

 sharp edges by means of corresponding depressions in the dorsal cup and 

 tegmen. Costals and distichals marked by rounded, longitudinal ridges, 

 following the median line of the plates. Ventral disk a little higher than 

 the dorsal cup, its lateral margins slightly bulging, the lower edge some- 

 what projecting over the upper margin of the dorsal cup. Plates flat, their 

 surface in well preserved specimens densely covered by fine granules. 



Infrabasals small, hidden by the column ; forming a flat pentagonal disk. 

 Basals rather large, about as wide as long ; curving abruptly upwards ; the 

 posterior one slightly truncated at the upper end ; the interbasal suture lines 

 distinctly grooved. Eadials twice as wide as long, their proximal ends dis- 

 tinctly angular. First costals much shorter and narrower than the radials ; 

 quadrangular. Second costals longer and a little wider than the first ; their 

 lateral faces short; the sloping upper faces making a right angle. First 

 distichals as large as the axillary costals, followed by two or three cuneate 

 plates in the calyx, which slightly interlock. Structure of the free arms not 

 observed, but they were apparently biserial and quite heavy and pendent. 

 First interbrachials of the regular sides the largest plates of the calyx, rising 

 to the height of the first distichals, and being succeeded by two rows of two 

 plates each. The anal plate a Httle higher than the radials, supporting three, 

 two, and two, smaller plates. Interdistichals one, small. Posterior oral nearly 



26 



