THYSANOCRINIDZ&. 213 
completely cover mouth and ambulacra, apparently without the assistance of 
orals. Anal side greatly protruding, forming an immense projection, which 
begins in the dorsal cup, and extends to over one third of the whole sur- 
face of the disk, giving to the specimen an exceedingly irregular form. 
The projection resembles an inflated sac, which toward the upper end 
grows decidedly smaller, and on approaching the summit turns abruptly up- 
wards in form of a good sized tube. The first anal plate rests upon the 
broadly truncated posterior basal, and is followed by three plates in the 
second, and three or more in the succeeding rows. Interdistichals 1, 2, 2; 
the lower plate resting upon the tpper sloping faces of the second distichals. 
The inflation upon the disk, as appears from the impressions, was covered by 
a large number of plates without definite arrangement. There were a few 
large plates, surrounded by smaller ones, all slightly convex and ornamented 
in a similar manner. Mouth excentric, marked in the casts by a stellate 
protuberance, from which the ambulacra pass out to the arm openings. 
Column unknown. 
Horizon and Locality. — Same as last. 
Siphonocrinus pentagonus W. and Sp. (nov. spec.). 
Plate XIX. Figs. 4a, b. 
A large species, of the type of S. nobilis, Calyx decidedly asymmetrical, 
about as high as wide, strongly lobed at the arm regions; the depressions 
deep and wide. Posterior side of the calyx enormously inflated from the top 
of the anal plate to the summit of the disk, the bulging involving the left 
posterior ray, which projects more conspicuously than the others. Dorsal 
cup obconical, the sides evenly spreading to the top of the costals, thence 
more rapidly to the arms. The upper angles of the basals and lower angles 
of the interbrachials more obtuse than in the preceding species, and never 
in contact. Radials, costals, and interbrachials of nearly uniform size; the 
first costal somewhat larger than the second. The first distichal as large as 
the upper costal, the two following considerably smaller, the succeeding ones 
free arm plates. Arm structure unknown. Interbrachials 1, 2, 5, followed 
by interambulacrals. The anal plate is succeeded by three and four plates, 
the latter supporting the plates of the anal protuberance, which on approach- 
ing the top of the disk contracts rapidly, and turning abruptly upward, forms 
a tube at the summit. Ventral disk one fourth shorter than the dorsal 
