322 THE MEDALS OF CREATION. Cuap. IX. 
fore, places the earliest type of Echinide at present known 
in the order Perischoechinide. The case is spheroidal, formed 
of more than twenty rows of plates; five ambulacra com- 
posed of two rows of pentagonal plates each ; rows of inter- 
ambulacral plates, three, five, or more, terminating dorsally 
in five large pentagonal ovarian plates. 
As in the more recent forms, these Cidarites are separable 
into two groups or families; one in which the spiniferous 
tubercles are imperforate as in the Echinus (Palechinide 
of M‘Coy); the other with numerous small secondary tu- 
bercles and a few large primary ones, perforated for the 
ligament of the spine as in Cidaris (the Archeocidaride of 
M‘Coy).* 
CLYPEASTRID#.—The shell in this family of sea-urchins, 
is oblong or rounded; the mouth is of an angular form, and 
situated in the middle of the base or inferior face; it is 
furnished with well-developed dental organs. The outlet is 
distant from the summit. The tubercles are mere granu- 
lations, and the spines proportionally small. This group is 
subdivided into two tribes; the GaLEeRiTiDZ (helmet-like), 
and the CiyPem® (buckler-like). 
GALERITES ALBO-GALERUS. Zign. 104.—The tribe of which 
this genus is the type has the shell inflated, orbicular, ob- 
long, or pentangular. The ambulacra are simple, never petal- 
loid ; the poriferous zones extend uninterruptedly from the 
summit to the mouth. 
In the species figured Zign. 104, fig. 1, the shell is of a 
conical form, in some varieties subpentagonal ; narrowest 
at the hinder part. The mouth is of a decagonal shape, and 
armed with teeth: it is situated in the centre of the base 
(Lign. 104, fig. 1°); the outlet is near the posterior margin 
of the base. The surface of the shell is covered with gra- 
* Prof. Sedgwick’s “British Paleozoic Fossils,” p. 124. 
