88 PROCEEDINGS OF THE ACADEMY OP [1886. 



5 and Y 6, on PI. xvi, that one of the tubercles was larger than 

 the others. The larger one may have been pierced by the anal 

 opening, for it occupies relatively the same position as the anal 

 opening in Haplocrinus. 



We cannot agree with Etheridge and Carpenter that Poterio- 

 crinus isacobus Austin, which we referred (Rev. I, p. 113) to 

 Scaphiocrinus, is an Allagecrinus. The little cup, which Austin 

 figured on PI. 8, fig. 4, of his Monograph, is evidently a ring of 

 underbasals, with a few stem-joints attached to it, and not basals. 

 To judge from the figures, there is in our mind scarcel}'' a doubt 

 that, in some way or another, the caly:s. in the type-specimen 

 became detached, that the basals and radials were lost, and the 

 underbasals temporarily fastened to the arms for safe-keeping. 

 Similar detached cups are frequently found in the Burlington 

 limestone, and we doubt if there will ever be found a species of 

 Allagecrinus with branching arms. 



Generic Diagnosis. Crinoid minute. Calyx p^'riform or 

 cylindro-conical. The dorsal cup composed of two rings of five 

 plates each ; the ventral surface, so far as known, of five single 

 pieces. There are no anal plates, neither dorsally nor ventrall3^ 



Basals five ; suture-lines rarely visible. Radials five, elongate, 

 variable in form and size ; they are either axillaries and support two 

 simple arms, or truncate above and bear a single arm, but neither 

 one of them is branching ; when axillaries, they are considerably 

 wider. The articular facets for the attachment of the arms are 

 large and distinct, and nearly horizontal in position, so as to 

 give a projecting lip-like appearance to the upper and outer 

 edges of the radials. There is a transverse articular ridge 

 around the opening of the central canal, which is large. The 

 arms are strong, cylindrical, and probably without pinnules. 

 The first arm-joint is much shorter than the others, cuboidal, 

 with a nearly circular distal face, the succeeding ones elongate, 

 three and four times as wide as high. 



The construction of the ventral surface is only known in the 

 younger specimens, in which it consists of five interradial plates, 

 which form a closed pyramid, the relative size of which is 

 greater the smaller the specimen. The plates are trigonal, but 

 the lower angles slightl}^ truncate to form the arm-opening. In 

 the smaller specimens, the plates are so closely united, that there 



