316 PROCEEDINGS OF THE ACADEMY OP [1881. 



of equal size. There is one in the first, and two in the suc- 

 ceeding series, the third series consisting either of one large or of 

 two comparatively small pieces, a fourth series is but rarely ob- 

 served. The posterior side has a special anal plate in line 

 with the first primary radials, and is of equal size with them.. 

 There are two plates in the second, smaller than the first inter- 

 radial at the other sides, and one, two or three plates in the 

 succeeding series, Interaxillary plates may be present or absent, 

 their number never exceeds three. 



The vault is composed of rather conspicuous plates, all proxi- 

 mal and radial dome plates nodose or tuberculous, the others 

 merely convex, with the exception of the centre plate, which is 

 prominent, larger than the rest, and which toward the anteiior 

 side forms the base of the anal tube. The tube is almost central, 

 strong, composed of heavy pieces, and sometimes extends bej^ond 

 the limits of the arms. 



Inner floor of the vault, along the interpalmar spaces, strength- 

 ened by braces, which increase in thickness outward, leaving open 

 galleries which diverge to the arm bases. There is a respiratory (?) 

 pore apparently at the side of each arm opening ; they however, 

 are but rarely observed, owing to imperfect preservation of the 

 arm bases. 



Column long, moderatel}^ heavy, its joints frequently sharply 

 edged ; central canal round or pentalobate, and of medium size. 



Geological Position^ etc. — The genus is strictly Subcarbon- 

 iferous, and has been found only in the lower and middle portions 

 of that formation. In America it does not extend vertically 

 beyond the Keokuk limestone ; geographical distribution wide. 



We recognize the following species : — 



1853. Actinocrinus armatus De Koninck and Lehon. Rech. Crin. Belg., p. 138, 

 PI. 4, figs. 4, a, b, c ; Meek and Worthen, Geol. Rep. 111., ii, p. 149. Mount, 

 limest. Toiirnay, Belgium. 



1869. Actinocr. asperrimus Meek and Worthen. (Strotocr. (1) asperrimus). Proc. 

 Acad. Nat. Sci. Phila., p. 160; also Geol. Rep. 111., v, p. 349, PI. 8, fig. 3. 

 Lower Burlington limestone (not Upper, as stated by Meek and Worthen). 

 This is a regular transition form between Aotinocrinus and Teleioorinus, but 

 as the rim is interrupted not only at the interradial, but also over the inter- 

 axillary spaces, we arrange it with Actinocrinus. 



1860. Actinocr. brontes Hall (Sect. A). Supp. Geol. Rep. Iowa, p. 47; Meek and 



Worthen, Geol. Rep. 111., v, p. 341. Keokuk limest. Keokuk, Iowa. 



1861. Actinocr. clarus Hall (Sect. B). Desc. New Sp. Crin., p. 2; also Bost. Journ. 



Nat. Hist., p. 277, Photgr. PI. 2, figs. 24, 25 ; Meek and Worthen, Geol. Rep. 

 HI., V, p. 341. Lower Burlington limest. Burlington, Iowa. 



