722 
PROFESSOR WYVILLE THOMSON ON THE ECHINOIDEA OE THE 
been very satisfactory. So very large a proportion of the species are extinct that the 
group comes rather within the domain of palaeontology than that of recent zoology ; and, 
as the two branches of the subject have not always gone hand in hand, some confusion 
has occurred. Among the fossil Cidaridse, palaeontologists have never regarded the 
smoothness or crenulation of the bosses of the primary tubercles as a character of generic 
value; and I believe they are entirely justified in disregarding it, for crenulation occurs 
in every possible degree, and we frequently find in a single specimen that some of the 
bosses are crenulated and others smooth. The contiguous or remote arrangement of the 
pores is also a very critical character. 
In the fossil genus Bhabdocidaris, Desor, in which the remote arrangement with the 
connecting-groove is most marked, it is always associated with very strongly crenulated 
bosses, and usually with elliptical areolae ; still, although the group thus distinguished 
has a certain characteristic facies and a definite distribution in geological time, I do not 
think it can be regarded as of more than subgeneric value. The genus or subgenus 
Phyllacanthus , Brandt, founded upon the form of the radioles chiefly, has no sufficient 
basis. The genus Leiocidaris, established by M. Desor for the reception of certain 
living species with remote pores and smooth bosses, seems to me to be valueless. In 
these the character derived from the arrangement of the pores is so obscure that several 
species (as, for example, the common Cidaris tribuloides) occupy an uncertain intermediate 
place, while certain subordinate characters (such as the comparatively large size of the 
areolse and the great length and the cylindrical form of the spines) are not constantly 
associated with it, and are shared by many fossils which still retain a place in the type 
genus. In his valuable 4 Revision of the Echini ,’ now progressing towards completion, 
Mr. Alexander Agassiz sets aside the genus Leiocidaris ; but he proposes, apparently 
for Cidaris pajpillata alone, the subgenus Dorocidaris , founded upon a number of some- 
what vague characters, all of them to be found singly and in different combinations in 
various fossil species of the genus Cidaris. 
This multiplication of names seems unnecessary ; I would therefore propose, at all 
events provisionally until it is in our power to revise the whole of the fossil series from 
a zoological point of view (an issue which, through the excellent work of Dr. Wright, 
M. Cotteau, and others, may not be far distant), to restore Leiocidaris and Phyllacanthus 
to the genus Cidaris , and likewise to relegate to the type genus the species now consti- 
tuting the genus Bhabdocidaris , retaining Bhabdocidaris , however, as a subgenus under 
Cidaris. Liplocidaris seems to have some claim to generic rank on account of its ten- 
dency to a bigeminal arrangement of the pores ; and possibly the same may be accorded 
to Goinocidaris from the singular sculpture of the test. Porocidaris is distinguished by 
a remarkable character, which is evidently of some physiological import, and also differs 
from Cidaris in other less important particulars. 
1. Cidaris papillata, Leske. (Plate LIX. figs. 1-13.) 
Principal synonyms: — Cidaris papillata, Leske ajmd Klein, 1778; Cidarites hystrix , 
