INVERTEBRATES. 225 



vault, and there are two false arms over the anal area, which are smaller than 

 the others, and stand one on each side of the summit of the anal space, there 

 heing thus six, instead of five, of the false arms in this species. These smaller 

 false arms are probably simple all the way out, while the larger ones probably 

 bifurcate. The anal opening "in this specimen is nearly midway between the 

 middle and the margin, and opens obliquely outwards, with slightly protuberant 

 margins. 



This species is more nearly related to Gilbertsocrinus tuber •culosus=(!Frema- 

 tocrinus tubercidosus, Hall, Sup. Iowa Report, page 75), than to any other with 

 which we are acquainted. It differs, however, in being proportionally higher, 

 and in having smaller and much less prominent subradials, which are but 

 slightly convex, and so short as to be scarcely visible in a lateral view; while 

 those of G. tubercidosus are described as being " produced into strong tubercu- 

 liform nodes," and extending up so as to form a part of the outer walls of the 

 body. It likewise differs in having its first radial plates merely rather dis- 

 tinctly convex, and larger than the subradials, instead of smaller and " strongly 

 tuberculiform." Again, it seems to differ in having the plates, especially 

 those of the interradials, somewhat excavated at the corners, so as to present 

 the appearance of a slight tendency to develope obtuse radiating costae at the 

 margins of the plates — a character not mentioned in Prof. Hall's description. 

 A more important difference, however, if we are not mistaken in regard to the 

 specimen we have mentioned as showing the summit, being identical with the 

 type of our species, is, that it possesses six instead of five false arms, owing, as 

 it were, to the division of the one on the anal side into two, each of which latter, 

 are only half the size of the others. Another difference is, the more lateral posi- 

 tion of the opening of the summit, and the connection of the anal series with 

 the vault above, in our species. 



Should Cumberland's name, OUacrinus, be adopted for this genus, the name 

 of this species will of course be OUacrinus fisceJIus. 



Locality and position : Lower beds of Burlington group of the Subcarbon- 

 iferous series. 



EGHINOIDEA. 

 PEEISCHOECHINID^]. 



{Synon. — Family Tesseles, Desor.) 



Rather widely different views are entertained amongst Zoologists and Palae- 

 ontologists in regard to the importance of the characters distinguishing the 

 Palaeozoic group of Echinodermata, under consideration, from the Mesozoic 

 29 Sept. 7, 1866. 



