274 PROCEEDINGS OF THE ACADEMY OP [1885. 



of them. It is difficult to believe that a plate so prominent, and 

 so universally represented among the older forms, should be un- 

 represented in the larva of recent Crinoids before the opening of 

 the oral pyramid. Carpenter's argument, that if the plate was 

 present in the larva it would be in the way, and have to undergo 

 resorption, is certainly not a strong one, for he admits in the 

 Urchins a partial resorption of the dorsocentral after the appear- 

 ance of the anus, and similar resorptions are going on constantly 

 in the growing Crinoid. 



Carpenter's arguments respecting the orals are based essentially 

 upon the existence of an orocentral plate, and if this cannot be 

 proved, his whole oral theory must fall to the ground. In the 

 recent Crinoids, he states : " The embiyological evidence clearly 

 indicates that the basals of the abactinal system are represented 

 in the actinal S} T stem bj r the orals. The former are within the 

 ring of radials and next to the dorsocentral ; and it seems, there- 

 fore, only natural to regard the six proximal interradial plates, 

 surrounding the central piece (orocentral) in the vault of a 

 Palreocrinoid, as representing oral plates.'' 



Admitting that the terminal plate at the base of the larval 

 stem in the Comatula3 represents the dorsocentral of Stellerids 

 and Urchins, a question which we will not discuss, and admitting 

 further, that a similar plate existed dorsally in the young Palaeo- 

 crinoid, which we have good reason to doubt, 1 we cannot make 

 out the affinities that are said to exist between this plate and the 

 central piece, the so-called "orocentral." The former is the 

 outer end of a mere transitory appendage, which in the growing 

 animal soon withers off, and which is attached to the outer 

 face of the skeleton, forming no part of it. The latter is a 

 permanent plate, which rests within the test and fills a con- 

 spicuous place in it. It is the most important plate in the 



1 We have examined a large number of roots, and have in our collection 

 five perfect Crinoids from the tips of the arms to the ends of the rootlets. 

 In all of them the column runs out into numerous branches, which all 

 come to a point, having no special terminal plate. It is evidetit that the 

 majority of the older Crinoids, either must have lived in a kind of oozy 

 ground, or they led a half-free life in the adult, using the root as an anchor. 

 In the Lower Silurian only we find attached to corals or shells isolated 

 disks, with a pit at the centre, which may represent the terminal plate- of 

 Glyptocrinus, but nothing like this has ever been found elsewhere. 



