1885.] NATURAL SCIENCES OF PHILADELPHIA. 251 



S. A. .Miller (Cinein. Soc. Nat. Hist., Dec, 1883), decribes as fol- 

 lows: " It is composed of numerous polygonal plates. Those in 

 the central part are the larger ones, and each of these bears a 

 central tubercle, which is sometimes prolonged so as to be desig- 

 nated a spine. Toward the margin, or rather following the undu- 

 lations toward the intertertiary areas, the plates are smaller and 

 possessed of slight convexity. They unite in the depressions in 

 the intertertiary areas with the plates of the calyx, or rather the 

 interprimarv radials graduate through the intersecondaries and 

 intertertiaries to the plates of the vault without any line of sepa- 

 ration. The plates become smaller as they approach the inner 

 face of the arms, over the swelling undulations of the vault, and 

 continuing to decrease in size, form a somewhat granular, con- 

 tinuous integument, that covers the ambulacra! furrows. This 

 continuation of the vault up the inner side of the arms, has been 

 observed for a distance of an inch above the vault, and, no doubt, 

 extended as far as the arm furrow itself." 



We have carefully examined Miller's original in Dr. R. M. 

 Byrne's collection, and can attest the correctness of his descrip- 

 tion. The decrease in the size of the plates toward the periphery, 

 which evidently led Carpenter to consider those plates as an out- 

 growth from the oral side, is readily explained by the enormous 

 accumulation of plates from the interradial, interaxillaiy and 

 interbrachial series, which terminate soon after entering the ven- 

 tral side, or else diminish in width. That the vault in Glypto- 

 crinus and Reteocrinus extends over the full length of the arms, 

 as suggested by Miller, and that only their large pinnules had 

 open food grooves, is at least doubtful, although it may be pos- 

 sible, as such is the case in the allied genus Melocrinus, in which, 

 however, the pinnule-like arms are provided with extra pinnules. 



Carpenter attaches considerable importance to our incidental 

 remark, " that the peculiar depressed state of the interradial and 

 interaxillary areas of Reteocrinus, the irregularity in the arrange- 

 ment of their plates, suggests the possibility that those parts 

 were adapted to expansion by the animal." And he makes use 

 of this as an argument in favor of his theory that the ventral 

 plates of Reteocrinus, like those of the Ichthyocrinidre, represent 

 " the plated perisome of the Neocrinoids." That the test of 

 Reteocrinus was in any way pliable, has been given up }>y us 

 entirely, nor do we believe that the pliable test of the Ichthyo- 



