310 PROCEEDINGS OF THE ACADEMY OF [1885. 



type, but also Ghjptocrinits Baeri Meek. These two species, how- 

 ever, have four basals, while the two former ones have five. 

 Equally close arc the affinities with Reteocrinus, which has well 

 defined underbasals. Xenocrinus, Reteocrinus, and Gli/ptocrinus 

 Richardsoni, which we make the type of our new genus Canistro- 

 crinus, agree in the following features : The plates of the live 

 main rays and their branches are formed into tube-like ridges 

 along the middle, with lateral extensions to meet the interradials. 

 The interradial areas are deepty depressed; composed of numer- 

 ous minute, irregularly arranged plates. The} r abut against the 

 basals and isolate the first radials to their full length. The 

 azygous interradius is divided by a conspicuous, rounded ridge, 

 composed of strong, comparatively large plates, longitudinally 

 arranged, which slightly decreasing in size, extend out to the 

 subcentral anal opening. 



Reteocrinus, Xenocrinus and Canistrocrinus constitute a natu- 

 ral, well defined group, and it seems to us impracticable to separate 

 them upon the ground that some of the species possess under- 

 basals. The lateral separation of the first radial plates distin- 

 guishes them from all Actinocrinidae, and this, according to P. 

 Herb. Carpenter, 1 " is a fact of considerable importance in Crin- 

 oid morphology ; but in this very character they approach some- 

 what the Rhodocrinites, in which, as a rule, the first interradials 

 all around meet the basals. Among the Rhodocrinites, however, 

 the lower interradials are perfectly regular plates, their position is 

 fixed, and they are succeeded by equally regular pieces. Whether 

 such widely different plates, as here represented, can be compared 

 with each other, is very doubtful, and this seems to have been the 

 opinion of Carpenter, who intimates that the irregular small pieces 

 of Reteocrinus can hardly be regarded as the complete morpho- 

 logical equivalents of the larger and more regular single inter- 

 radials which occur in the Rhodocrinidae." That these irregular 

 interradial plates occur in none of the later groups of the Palaeo- 

 crinoidea, but only in the very earliest Silurian types, and under 

 decidedly similar conditions, in species with and without under- 

 basals, points clearly to the conclusion, that those genera consti- 

 tute a little group by themselves, and we think this justifies us in 



1 On a New Crinoid from the Southern Sea by P. Herb. Carpenter, M. A., 

 Philos. Tians. of the Roy. Soc, Part III, 1883. 



