130 PROCEEDINGS OF THE ACADEMY OF 



nearly entirely received within the sinus, in the upper margin of the first 

 radial pieces. First anal and first interradial plates of apparently ahout the 

 same size, the former connecting with a range of small plates above, which 

 form the under margin of the lateral anal opening. 



The arms, after the first division on the second radial plates, divide again 

 on the second piece, above which the two inner branches bifurcate again on 

 the second piece, thus making six arms in each ray seen in the specimen 

 under description. Above the last division the arms are slender, very gradu- 

 ally tapering, and each composed of a double series of small alternating pieces, 

 (excepting near the points of bifurcation,) and support on their inner side 

 rather closely set ranges of tentacles. The column is a little compressed, and 

 composed of rather thin pieces, with prominent crenulated margins near the 

 base. 



Locality and position. Burlington, Iowa. Burlington Limestone. Collec- 

 tion of Charles Wachsmuth. 



Genus FORBESIOCRINUS, Koninck and Le Hon. 



Fokbesiockinds Moxeoensis. Body below the free arms apparently skort- 

 turbinate, or subglobose, composed of nearly smooth, rather thick plates, 

 connected by linear sutures. Base small, and nearly hidden by the column. 

 Subradial plates of moderate size, four of them pentagonal, and one on the 

 anal side apparently hexagonal, with unequal sides. First radials about 

 twice as wide as high, hexagonal in form, and nearly twice as large as the 

 subradials. Second, third and fourth radials, in two of the rays, (and the 

 fifth and sixth in another,) all nearly of the same length, hexagonal in form 

 and about twice as wide as long. Last primary radial pieces of nearly the 

 same size as the others, and supporting on their superior sloping sides the 

 secondary radials. 



Of the numerous interradials, the first is about the size of the subradial 

 pieces, hexagonal in form, and supports two smaller pieces in the second 

 range. Above these four or five occur in the next range, in one interradial 

 space, which is as far up as they can be counted in the specimen examined, 

 though it is evident from the breadth of the interradial spaces, that they must 

 increase at the same rate for several ranges above. (Anal plates unknown.) 



The column is rounded and comparatively thick at its junction with the 

 base, from which it tapers gradually towards the lower extremity. Near the 

 base it is composed of extremely thin, equal segments, connected by minutely 

 crenulated sutures. Farther down it gradually passes into a series of alter- 

 nately thicker and thinner pieces. 



After the first division of the rays on the last primary radial pieces, the 

 arms divide several times, and appear to give off lateral branches, but our 

 specimen is not in a condition to enable us to determine how many pieces in- 

 tervene between the points of division, nor do they show whether or not there 

 are any interaxillary pieces. 



The specimen before us presents the peculiar and anomalous appearance of 

 having a small false arm arising directly from the summit of the upper trun- 

 cated side of the largest subradial piece. It seems even to be inserted into a 

 sinus in the upper side of the subradial, yet we can scarcely believe it is any- 

 thing but one of the smaller divisions of the arms, accidentally broken off and 

 placed in that position. 



As near as we can determine from a description alone, this species appears 

 to be somewhat closely related to F. exculptus, ( Onychocrinus exsculptus, Lyon 

 and Cassiday, Am. Jour. Sci. vol. 29, N. S. page 78,) but differs in having less 

 produced basal pieces, while the upper angles of the subradials are obtuse 

 instead of "quite sharp." It also seems to have two or three more primary 

 radial pieces in one ray than occur in any of those of the species described by 

 Lyon and Cassiday. Again its surface appears to be smooth instead of granu- 



[Juue, 



