66 Dr. T. Wright on Fossil Echinoderms 
belong to what we regard as the typical form. This remark- 
able exceptional specimen agrees with the brief notice of C. 
Tauricus*, Desor:— Trés grande espéce, allongée, pentagonale, 
a bord fortement renflé. Zones poriféres trés large & leur ex- 
trémité. Tert. du Taurus, ile de Créte.” If we are correct in 
referring all these varieties to C. altus, it follows that this species 
has a wide range of deviation from what we take to be its typical 
form ; but these limits of variation are probably not greater in 
this than in some other species of Urchins. The following 
table shows the relative dimensions of three forms,—the typical, 
the conical, and the flattened and tumid varieties :— 
Forms. Length. Breadth. Height. 
Type specimen .........++. 5 inches. | 434,inches. | 23 inches. 
Conical, var. d. ...cseceeee- 585 5 a3, 435 55 
Tumid, var. 0. c.ccccscoces 655; Oe 55 Qwty ay 
The ambulacral areas are largely petaloid, nearly equal in 
length and width; they are rounded, widely open below, 
and extend over four-fifths of the dorsal surface in the type 
form, over nearly three-fourths in the conical form, and over 
almost four-fifths in the tumid varieties; in all, the areas form 
prominent convex elevations of the test, which are bounded 
by wide poriferous avenues, composed of two series of simple 
pores united by oblique grooves; the internal series of pores are 
round, the external series are elongated transversely in the 
direction of the grooves; the pores at the end of the avenues 
are much more so than those of the summit; the apical dise 
is small, and occupies the centre of the dorsal surface, lying in 
a slight depression formed by the bending-in of the summits of 
the areas; those of the single area, and the antero-lateral and 
postero-lateral areas of the left side, beg rather more pro- 
minent than those of the right side of the test. The madre- 
poriform body occupies the whole surface of the disc, the ocular 
and genital plates being quite indistinguishable from the general 
structure of the test; the five genital pores pass obliquely into 
the interior, at a short distance from the disc. 
The base is flat, and the mouth lies in a very deep depression 
in the centre of the under surface ; the opening is pentagonal, 
its wide walls being formed by the incurving of the basal por- 
tions of the areas; from each of the angles of the pentagonal 
opening, a deep furrow passes outwards towards the margin of 
the test, and becomes continuous with the median suture of the 
* Cat. raisonné des Echinides, Ann. Se. Nat. tom. vii. p. 131. 
