INVERTEBRATES. 241 



rays) a triangular outline, the lateral angles being probably 

 sometimes truncated. First anal plate narrow below, and 

 wedged down obliquely between one of the subradials and an 

 inferior sloping side of one of the first radials ; supporting one 

 or two smaller pieces above, the exact forms of which cannot 

 be made out in our specimen. 



Arms rather flattened on the outside, and after dividing on 

 the second radial pieces (in those seen), bifurcating again on 

 the sixth piece ; beyond this entirely simple, and each com- 

 posed of a single series of pieces, which are slightly wider than 

 long, and a little wedge-shaped, or alternately longer and 

 shorter on opposite sides. On the long side they project a 

 little above, for the reception of the tentacles, which are large, 

 and composed of joints nearly twice as long as wide. Height 

 to the summit of the second radials, about 0.17 inch; breadth 

 at the top of the first radials, 0.27 inch ; length of arms. from 

 their division on the second radial pieces, about 0.84 inch. 



This species seems to be related to Z. bifurcatus, of McChesney (Descr. New 

 Palaeozoic Fossils, p. 9, pi. 5, fig. 3), but differs in being less robust, and in hav- 

 ing proportionally broader subradial pieces, while the upper angle of its second 

 radials is much more salient, and the pieces between the first and second bifur- 

 cations of its arms, are more wedge-shaped than is represented in the figure and 

 diagram of Z. bifurcatus. The arms, or at least some of them, in Prof. McChes- 

 ney's species, also bifurcate a third time, while in our species, they are entirely 

 .simple after the second division. 



If, as has been suggested by Dr. Shumard and Mr. Lyon, the type of de 

 Koninck and Lehon's genus Graphiocrimis, should be found to possess the same 

 structure as Troost's Zeacrinus, de Koninck and Lehon's name, having priority, 

 will have to take precedence, and the name of this species will have to be written 

 Graphiocrinus planobrachiatus. 



Locality and position : Near south line of Monroe county, Illinois; Keokuk 

 group, of Subcarbbniferous series. 



31 Sept. 10, 1SG6. 



