930 
ME. P. H. CARPENTER ON A NEW 
I. Radials completely separated laterally, either by single 
interradial plates, or by groups of small ones. 
a. No ridges on the radials. 
/3. With ridges on the radials. 
II. The two posterior radials separated by an anal plate 
which rests on a basal. 
III. Radials in contact all round the calyx. 
Rhodocrinites (W. and S.) 
Archceocrinus. 
Reteocrinus. 
Glyptasterites (W.and S.) 
Glyptocrinus. 
I cannot help suspecting, however, that Zittel’s arrangement of these genera into 
two families, Glyptocrinidce and Rhodocrinidce, is the most natural one; though I 
should place Thylacocrinus in the latter, and not in the former as he has done. 
Postscript. 
(Added February 1, 1884.) 
During the past year the peculiarities of Thaumatocrinus have naturally been much 
in my mind, and I have been led to believe that the structure which I have called 
the anal appendage is represented in other Palaeocrinoids besides the two Silurian 
genera already mentioned. 
Wachsmuth and Springer'" describe Taxocrinus and Onychocrinus as having a 
small lateral proboscis in the anal area, which consists of a series of from two to six 
narrow quadrangular plates, longitudinally arranged, and resting on the upper surface 
of a basal. Meek and WorthenI spoke of it in Onychocrinus as “ really looking very 
much like a diminutive arm rising from the anal area and they subsequently found 
the remainder of the anal interradius to be occupied by a great number of minute 
irregular plates, which pass gradually upwards into those of the “ vault,” just as in 
Reteocrinus and Xenocrinus. If Thaumatocrinus were a larger type, with plated 
perisome between the rays, as in Pentacrinus asteria, its tapering anal appendage 
would be in the same condition as that of Onychocrinus, becoming merged above into 
the general plating of the anal interradius. 
I do not think, therefore, that Wachsmuth and Springer are quite correct in 
describing Taxocrinus and Onychocrinus as having “ a small lateral tube.” That the 
arm-like series of plates supported the lower portion of the anal interradius is doubtless 
true. But I do not imagine the plates to have been in any way hollowed on their 
inner sides for the reception of the hind-gut. This undoubtedly opened to the 
exterior at a higher level, through a regular anal tube just as in other Crinoids. 
* Revision. I., pp, 46-53. 
f 1 Paleontology of Illinois,’ vol, ii., p. 243 ; vol. in., p. 494. 
