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. 
Remarks. — The genus has its closest relations with Thysanocrinus, 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, Vol. X. (September), p. 138. 
Syn. Cyphocrinus Gorbyi 8. A. Miter (October 26, 1892). Adv. Sheets 18th Rep. Geol. Surv. 
Indiana, p. 51, Plate 7, Figs. 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 
tezmen. 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. Radials 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 little higher than the radials, supporting three, 
two, and two,smaller plates. Interdistichals one, small. Posterior oral nearly 
26 
