388 PALAEONTOLOGY OF ILLINOIS. 



American, it is also worthy of note that the surface of the body plates 

 is never ornamented with proper radiating costse, such as we often see 

 in Actinocrinus and other allied types, nor yet smooth, or properly 

 tuberculiform, as in Dorycrinus, but always presents a peculiar ver- 

 micular style of sculpturing or corrugation difficult to describe, but very 

 characteristic and easily recognized again after being once observed. 



To this group Mr. WACHSMUTH has in MS. correctly referred the fol- 

 lowing American species, viz : Amphoracrinns divergens, A. planobasalis, 

 A. spinobrachiatus ? and A. inflatus, described by Prof. HALL under 

 Actinocrinus; also Actinocrinus quadrispinus, White; all from the lower 

 division of the Burlington beds. 



AMPHOKACKIKUS DIVERGED, Hall (sp.) 



PI. 6, Fig. 6. 



(Proceed. Acad. Nat. Sci., Phila., 1868, p. 348.) 



Actinocrinus divergens, Hall. Supp. Iowa Report, p. 36, 1860. 



This species was apparently described by Prof. HALL from imperfect 

 specimens, showing only a few of the lower bifurcations of the arms, 

 since he thought it probably had only twenty-two arms, while perfect 

 specimens in Mr. WACHSMUTH'S collection show that they continued 

 bifurcating farther up, so as to make the whole number about fifty-three 

 or more, as already stated in another place. 



Amongst Mr. WACHSMUTH'S specimens there is one (No. 156) with 

 arms, body, vault and proboscis all in a remarkably fine state of pre- 

 servation, which appears to agree very closely with the A. divergens in 

 most of its characters, and yet differs in several respects. It has very 

 nearly the same number of ultimate divisions in the entire series of 

 arms, though there are differences in the details of their mode of divi- 

 sions, so that the number of arms in any one of the rays is different 

 from what we see in the corresponding ray of A. divergens. In each of 

 its posterior rays there are, as near as can be made out, thirteen to 

 fifteen arms ; in one of the lateral rays and the anterior one, each eight, 

 and the other lateral one eleven or twelve. Its ventral tube (proboscis) 

 is rather stout, about one inch in length, and crowned by some six or 

 seven small unequal spines, subspirally arranged. At the anterior side 

 of the base of the proboscis, and nearly at the center of the vault, there 

 is a large tumid piece, and on each side of this a spine about three- 

 fourths of an inch in length, directed obliquely outward, upward and 

 forward, and in front of these two other prominent or subspiniform 

 pieces. In the typical A. divergens, these two anterior lateral larger 

 spines each bifurcate, while in the specimen under consideration they 



