DISCOIDEA CASTANEA. 320 
outlet on the margin, occurs in the Chalk-marl of Sussex, 
Dorset, and the Alps; a specimen is figured in Zign. 106. 
Lien. 106. Disco1pEa (Galerites) cASTANEA. Chalk-marl, Dorset. 
Fig. 1.—Profile. The pores and plates of the ambulacra only are 
inserted in this figure. 
2.—View from above. 
3.—The base, showing the central pentangular mouth, and 
the vent in the margin. 
The Ciypeme® differ from the tribe of echinites last 
described, in the ambulacra being petaloid, that is, of a leaf- 
like shape, and disposed in a stellated figure on the upper 
part of the shell. The ambulacra do not extend to the 
mouth. The shell is generally of a depressed form ; and the 
petaloid ambulacra in many species appear like an elegant 
star, richly fretted, spread over the shell. There are nume- 
rous species of this type, both recent and fossil ; many of 
the latter, being of a large size, are beautiful objects in a 
cabinet of petrifactions. 
Ciypeus stnuatus (Pict. Atlas, pl. liv. fig. 1).— Of this 
genus, which is the type of the tribe, a large species, C. 
sinuatus, is very common in the Oolite of Wilts, Gloucester- 
