1886.] NATURAL SCIENCES OP PHILADELPHIA. 159 



1849. P. crassimanus McCoy (not P. crassimanus Eichw.), Ann.and Mag. Nat. Hist. 



(Ser. ii),vol. iii, p. 245. Contrib. Paliuont., p. 106. Carboniferous, Derbyshire. 

 1882. P. illinoisiensis Worthen, Bull, i, 111. St. Mus. Nat. Hist., p. 10 ; also Geol, 



Rep. Illinois, vii, p. 289, PI. 28, fig. 17 Warsaw limest. Warsaw. 111. 

 1844. P. inequidactylus McCoy, Carboniferous Foss. Ireland, p. 179, PI. 26, fig. 8. 



Carboniferous. Ireland. 

 P. minimus Austin (not Ad. Roemer) is probably a synonym of Scaphio- 



crinus isacobus. 

 1882. P. similis Worthen, Bull, i, 111. St. Mus. Nat. Hist., p. 23; also (Jeol. Rep. 



Illinois, vii, p. 295, PI. 30, fig. 12. Kaskaskia limest. Monroe Co., 111. 



This is evidently a young specimen, probably of one of the other species. 

 1882. P. validus Worthen, Bull, i. 111. St. Mus. Nat. Hist., p. 18 ; also Geol. Rep. 



Illinois, vii, p. 287, PI. 28, fig. 16. Warsaw limest. Warsaw, 111. 



SCAPHIOCRINUS Hall, Rev. I, p. 112. 

 (Emend. W. andSp.) 



Dorsal cup obcoiiical to semi-ovoid ; all its plates closel}' united 

 by suture. Radials truncate above, the articular ridge filling 

 almost the entire width of the upper face. Brachials long, simple 

 or compound, similar in form to the radials but truncate below; 

 line of articulation gaping. In species with compound brachials, 

 the two segments have the form and proportions of the one plate 

 in the others, and are joined by suture. Arms long, branching; 

 arm joints rather long, wedge-form. Azygous side as in Poterio- 

 crinus. Column obtusely pentagular. 



Poteriocrinus Jesupi Whitfield, Amer. Mas. Nat. Hist. N. Y., 

 Bull, i (Decbr., 1881), is evidently a synonym of P. Swallovi M. 

 and W. (compare 111. Rep., ii, PI. 16, fig. 4), although Whitfield 

 thinks it distinct in the bifurcation of the arms, and in the number 

 and arrangement of the anal plates. In the type specimen of P. 

 Swallovi only two bifurcations of the arms were preserved, and 

 Meek and Worthen remarked on p. 84, that the arms in the upper 

 parts " seemed to be simple " in this species. The latter is not 

 confirmed by our specimens, of which many have arms and ven- 

 tral sac beautifully preserved ; they all show essentially the same 

 bifurcations as Whitfield's specimen. Slight variation in the num- 

 ber of arm joints in one of the bifurcations cannot be regarded 

 as a good specific character, and even an additional division 

 of the arms may take place in the same species. The apparent 

 variation in the number of " anal " plates is explained by the fact 

 that in the type of P. Swallovi the arms accidentally cover the 

 lower portion of the ventral sac, exposing to view only four plates ; 

 while in Whitfield's specimen a much greater portion of the ven- 

 tral sac is visible. 



