51 
diminished by the fact that they were not made, as Neumann’s 
were, on fresh specimens. 
On the MINUTE STRUCTURE of CERTAIN HARD PARTS of the 
Genus Ciparis. By Cuarzes Stewart, F.LS., F.R.M.S. 
(With Plate LV.) 
iy we regard a natural classification of echinoderms as an 
indication of their genetic relationships, it requires all points 
of their development and structure to be known; but as so 
complete a knowledge as this is rarely attained, some feature, 
whose modifications are easily recognised, generally has un- 
due importance attached to it. In the hope of contributing 
to a more satisfactory classification of the recent regular 
Echinoidea, I have devoted some time to the minute anatomy 
of this group of Echinoderms, and have found a remarkable 
constancy in their minute structure, by which species appear- 
ing closely allied can readily be distinguished, and groups as 
clearly indicated as by their more marked features. But I 
should wish it to be thoroughly understood that I in no way 
underrate the value of those parts of their anatomy which 
have long been used in determining the families genera and 
species: my object is rather to direct attention to some cha- 
racters whose importance has not I think been fully recognised. 
The suborder of recent Echinoidea Regularia is divided 
into four families, namely, Cidaride, Diademide, Echinide, 
and Echinometride. These are, however, not of equal im- 
portance, and leave many groups of associated genera, of 
which one may speak as sub-families. 
I have selected for the present paper Cidaris annulata to 
represent the restricted genus Cidaris (C. Thouarsii, C. 
tribuloides, C. baculosa, C. annulata), this being a leading 
example of the first family, hoping to give the remaining 
genera on a future occasion. 
Spines.—The spines of the Cidaride are of two sorts, 
primary and secondary. ‘The primary spines, by far the 
larger, are arranged one on each plate of the interambulacral 
areas, to which they articulate by a ball-and-socket joint. 
The joint is surrounded by a muscle to move the spine ; there 
is also a small muscle or ligament, extending from a pit on 
the ball to a pit on the concave articular surface of the spine. 
The secondary spines are much more numerous, and are 
