CRINOIDS AND BLASTOIDS. 167 



portion of the vertical suture which unites the two series of the 

 arm. Pinnules long, constructed and arranged as in A. orna- 



tisshuus. 



Interradials five to seven up to the arm bases. The first is 

 hexagonal, in size equal to the second radials. The second and 

 third ranges consist of two pieces, which are comparatively 

 large. First anal plate about the size of the first radials, but 

 angular above instead of truncated. It supports two interra- 

 dials. succeeded by ranges respectively of three, two and two 

 plates. There is one interaxillary, but no interbrachial piece. 



The ventral side is hemispherical, composed of a large number 

 of very small, smooth plates, interspersed with prominent 

 spiniferous ones representing the summit plates. The various 

 summit plates are separated from one another by the smaller 

 pieces, as in Mcgixtocrinus. and so are also the different orders 

 of radials. which are represented likewise by spiniferous plates. 

 The central plate forms the base of the ventral tube: the latter 

 is located almost centrally, and does not extend to the tips of 

 the arms. 



The surface of the plates on the dorsal side is marked by 

 numerous broad, indistinct ridges, passing singly or in pairs 

 from the middle portions of the plates to adjoining pieces. 

 Those connecting the radials and ascending to the arm bases, 

 are not stronger than any of the others, a character by which 

 this species is readily distinguished from A. ornatissimus. 



Column round, moderately strong, and composed of alter- 

 nately large and small joints, rounded at their edges. In a 

 specimen in our collection, apparently of full growth, in which the 

 column is preserved to its termination, it is about fifteen inches 

 long. The upper half of the stem is stouter than the lower half, 

 which ultimately terminates in a sharply pointed root. At the 

 upper end. the nodal joints project largely over the intermediate 

 ones, which are also shorter, but the latter grow gradually in 

 length and width, until at the middle of the stem they equal in 

 size the nodal ones, which appear to be correspondingly somewhat 

 diminished. This change goes on more rapidly toward the end of 

 the stem, where the joints lose that convexity which is so marked 

 in the proximal region, and become uniform. The lower por- 

 tions of the stem are provided with a few thread-like lateral 



