738 
PROFESSOR WYVILLE THOMSON ON THE ECHINOIDEA OF THE 
1. Calveria hystrix, sp. nov. (Plates LXIV. & LXV.) 
The test is circular and depressed. The calcareous plates are very thin, but they are 
imbedded in a firm leathery perisom, so that the body-wall is tough and resistant. The 
only perfect specimen of the species procured is 130 millims. in diameter and about 25 
millims. in height. The interambulacral areas are about one third wider than the 
ambulacral. The peristome is 35 millims. in diameter, and the periproct 20 millims. 
from the outer edge of an ocular plate to the outer edge of the ovarial plate opposite. 
Both the apical and the oral surfaces are nearly flat. The edge is round and full, with 
no tendency to become angular ; and the plates, both ambulacral and interambulacral., 
retain, in passing round the edge, the same character, both as to form and position and 
as to the distribution of primary and secondary tubercles, which they have on other 
parts of the test. The number of interambulacral plates in a row extending from the 
edge of the peristome to that of the periproct is about forty-four, and that of the ambu- 
lacral plates considerably greater, as very frequently two ambulacral plates terminate 
under one interambulacral plate. Near the circumference, on the oral surface, the inter- 
ambulacral plates are 25 millims. in length, and the narrowest part of the plate is 2*5 
millims. in width, expanding at the middle line to 4 millims. The narrow strap-shaped 
portion of the plate occupying the outer part of the interambulacral area is 20 millims. 
in length, and the wide expansion which over- or underlaps the like expansion of the 
corresponding plate on the other side of the area in the middle line is about 5 millims. ; 
so that although the total length of each interambulacral plate is 25 millims., the total 
width of the area is not much more than 40 millims. Each plate is rounded and some- 
what expanded towards the outer edge, where it covers the end of one or of two ambu- 
lacral plates ; and at this point it bears a primary tubercle with a large smooth scrobicular 
area. It then continues for about two thirds of its length narrow and strap-shaped, 
bearing a few secondary tubercles and miliary grains. It then expands again and bears 
another primary tubercle not quite so large as the former, and then abruptly curves 
towards the oral pole, passing in that direction under the expanded end of its fellow on 
the opposite side. The outer surface of the expanded portions of the plate, in the centre 
of the area, is also studded with miliary granules (Plate LXV. figs. 1 & 2). 
The strap-shaped portions of the plate between the two primary tubercles is so much 
narrowed that the plates of a series are not in contact at this point, a narrow linear 
space being left between them, closed only by the soft perisom and the membrane in 
which the calcareous plates are formed. 
The ambulacral plates are much narrower than the interambulacral. They likewise 
have narrow fenestrse between them towards their outer ends, and they overlap, though 
not to so great an extent, in the centre of the ambulacral area. Each ambulacral plate 
is studded with secondary tubercles and miliary granules, and at about two thirds of its 
length from the outer edge it bears a small primary tubercle. As in Phormosoma, the 
double pores are arranged in arcs of three, and, as in that genus, the two inner pairs of 
pores pass through special pore-plates intercalated between the ambulacral plates, while 
