1885.] NATURAL SCIENCES OF PHILADELPHIA. 347 



Arms long, of nearly equal thickness throughout their length. 

 They are composed of two series of very short pieces, alternately 

 arranged. Ventral furrow wide and deep. Pinnules long, closely 

 packed together, composed of six to seven joints, three times 

 longer than wide. 



Interradials three, in two series ; the first series composed of 

 two plates, which rest upon the belt of the supplementary inter- 

 vening pieces already described, and between the sloping sides of 

 the second radials. The second series consists of a single piece, 

 placed between the upper sloping sides of the first radials, and 

 the lower sloping sides of the second radials. The azj-gous side 

 is known onby in A. Wortheni. In that species it is composed of 

 two hexagonal anal plates, resting upon a row of similar pieces, 

 which, like those, are longitudinally arranged. The upper anal 

 plate is placed in line with the second primary radials, and is higher, 

 but not quite so wide ; the second plate is somewhat smaller. At 

 each side of the anal plates there are three interradials, which are 

 formed and arranged like those of the four other sides. 



The ventral covering is but imperfectly known ; we only observed 

 numerous thin, very minute, irregular pieces, with an elevation 

 toward each ray. Position and form of the anus unknown. 



Column round, somewhat tapering downward, composed of 

 thin joints ; central canal small. 



Geological Position, etc. — Acrocrinus is the last and only sur- 

 viving genus of the Camarata at the close of the subcarbonil'erous. 

 It has been found only in the Mississippi valley, where it is 

 exceedingly rare. 



1855. A. Shumardi Yandell. Type of the genus, Amer. Journ. Sci. and Arts, vol. xx 

 (new ser.), p. 135 with figure. (It was previously figured without descrip- 

 tion or name by Yandell and Shumard, 1817, in their Contrib. Geol. Ken- 

 tucky, PI. 1, fig. 3). — Chester or Kaskaskia liinest. Grayson Co., Ky. 



1858. A. urnaeformis Hall. Geol. Rep. Iowa, i, PI. ii, p. 690, PL 25, fig. 11 a, b.— 

 Chester or Kaskaskia limest. Pope Co., 111. 



1882. A. Wortheni Wachsmuth. Bull, i, 111. .St. AIus. Xat. Hist., p. 41; also Geol. 

 Rep. 111., vii, p. 343, PI. 30, fig. 13.— Coal measures. Peoria Co., III. 



Family IX.— BARRANDEOCRINID.E Angl. 



BARRANDEOCRINTJS Angl. 



This is one of the most remarkable forms of the Paloeocrinoidea. 

 Looking at a perfect specimen with all its arms intact, it super- 



