NATURAL SCIENCES OF PHILADELPHIA. 391 



radial plates slightly larger than the first, wider than long, pentagonal, and 

 indistinctly hexagonal ; all longer on the inferior truncate side than either of 

 the others; apparently four of them supporting on their superior sloping sides 

 the first divisions of the arms, while the one on the anterior side is truncated 

 above, and succeeded by three other very short, wide pieces, upon the last of 

 which the first divisions of the arms rest. 



Only two of the anal pieces are seen in the specimen examined ; one of these, 

 which is small, occupies a position partly between the right superior sloping 

 side of the largest subanal piece, and the left inferior sloping side of one of 

 the first radials. The other connects wiih this on the left, and rests upon the 

 left upper sloping side of the large subradial piece, being apparently flanked 

 on its left side by one of the first radial pieces. 



The arms are nearly flat, or but slightly rounded on the outer side, and 

 bifurcate again, after the first division on the second radial pieces (in the 

 lateral and posterior rays), on the eighth, tenth, and eleventh pieces, and one 

 of the subdivisions again divides on the twelfth or fourteenth piece, beyond 

 which they are all simple. 



Named in honor of Dr. G. Troost, deceased, former State Geologist of 

 Tennessee. 



Locality and yjosition. Cedar creek, Warren county, Illinois. Burlington 

 Limestone, of subcarboniferous series. 



Zeacrinus planobrachiatus. Body small, depressed, basin-shaped, concave 

 below, rapidly expanding upwards, composed of apparently smooth plates, 

 connected by moderately distinct sutures. Base small, and placed within the 

 concavity of the under side; columnar facet very small. Subradial pieces 

 as wide as long, or a littte wider, four pentagonal, and one on the anal side 

 hexagonal, having one angle slightly truncated. First radial pieces wider than 

 long, expanding from the base, pentagonal, the upper side being horizontally 

 truncated, and longer than either of the others. Second radial pieces nearly 

 as large as the first, presenting a triangular outline (in the posterior and lateral 

 rays), the lateral angles being probably truncated ; supporting on their 

 superior lateral sloping sides the first divisions of the arms. First anal plate 

 narrow below, and wedged down obliquely between one of the subradials and 

 the inferior sloping side of a second radial ; supporting another piece on its 

 left superior sloping side, and apparently a smaller one on its narrow truncated 

 upper extremity. 



The arms are rather flattened on the outer side, and after the first division 

 on the second radial pieces (those seen), bifurcate again on the fifth and sixth 

 pieces. Beyond this they are entirely simple, and composed of a single series 

 )f pieces, which are slightly wider than long, and alternately longer and 

 shorter on opposite sides. On the longer side they project a little above, for 

 the reception of the tentacles, which are composed of joints nearly twice as 

 long as wide. 



Height from base to summit of first radials, 0-13 inch ; breadth at the top of 

 first radials, 0-27 inch ; length of arms, from their division on the second radial 

 pieces, about 0-94 inch ; length to bifurcation on the sixth piece, 0-19 inch. 



Locality and position. Monroe county, Illinois. Keokuk Limestone^ of low er 

 arboniferous series. 



Genus CYATHOCRINUS Miller. 



Cyathocrincs Saffordi. Body subglobose, wider than high, the broadest 

 part being below the middle, unsymmetrical, the anal side being longest, and 

 most gibbous ; composed of thin, smooth plates, joined by slightly raised, 

 linear sutures. Base of moderate size, irregularly pentagonal, flat, or so slightly 

 convex as to be scarcely seen in a lateral view, consisting of unequal, sub- 

 hexagonal plates, the lateral and outer margins of which are nearly equal, 

 while the side next the column is so short as to appear to terminate in an 



I860.] 



