328 PROCEEDINGS OF THE ACADEMY OP [1881. 



Interradials three, of moderate size, the two upper ones situated 

 within the sinus formed by the extended rays, Anals three to four 

 large ones, succeeded by additional smaller ones ; the first in line 

 with the first radials; the second series two, rarely three. In the 

 construction of the anal side, Amphoracrinus forms a link between 

 the Actinocrinites and Agaricocrinites. In this respect it is 

 interesting to observe that the second series of plates, within the 

 limits of the same species, has sometimes two, and sometimes 

 three plates, but wherever the third plate is present, it is narrower 

 and smaller, and touches the first anal but slightly; while when 

 absent, the plate above them falls in deeply between the two plates. 



Dome high, inflated, the interradial spaces depressed, the radial 

 portions formed into broad ridges, which increase in prominence 

 toward the arm bases. Central dome, and the four large proximal 

 pieces placed in contact with each other, large, and strongly 

 spiniferous (the spines in A. divergens Hall sometimes attain a 

 length of an inch and a-half, and are bi- or tri-digitate), the two 

 smaller proximal plates are separated by a wide, somewhat inflated 

 area, which supports an anal tube. The tube is located in the rear 

 of the central plate and is almost central, while the central plate 

 is pushed somewhat to the anterior side. The tube is constructed 

 of plates similar to those of the vault ; it is rather stout through- 

 out, but very short, its upper extremity rounded, with a small 

 subcentral anal opening, which is surrounded by plates and spines, 

 similar to those which surmount the vault at the base of the tube, 

 but on a smaller scale. The other plates of the dome are of nearly 

 equal size, their sui'face beautifully granulated. Inner floor of 

 the vault as in Actinocrinus^ deeply grooved along the radial 

 portions, and formed into closed galleries toward the arm bases. 



Column round, constructed alternately of larger and smaller 

 joints, whose lateral margins are sharply edged ; central canal 

 small. 



Geological Position^ etc. — Amphorocrinus occurs only in the 

 lower strata of the Subcarboniferous — not beyond the age of the 

 Lower Burlington limestone — both in America and Europe. 



We recognize the following species : — 



»1849 (?). Amphoracrinus atlas McCoy. (Aotinocr atlas) Ann. and Mag. Nat. Hist. 

 (ser. ii), vol. iii, p. 246; Roemer, 1865, Amphoracr. atlas, Lethsea Geogn. 

 (Ausg. 3), p. 250. Mount, limest. Holland, Engl. 

 Perhaps Syn. of Amphoraor. Gilbertsoni Austin. 



