324 THE MEDALS OF CREATION. Cuap. IX. 
when filled with flint, yield exquisite casts, if the shell be 
dissolved in dilute hydrochloric acid; by this means the 
form of the plates, and casts of the minutest ambulacral 
pores are obtained. 
Hotectyrvs (Galerites) inrLatus. Lign. 105.—In certain 
kinds of Galerites, the shell is strengthened internally by 
five strong ribs or projections, which of course leave cor- 
responding deep furrows or channels on the flint casts 
moulded in them; such fossils are not numerous on the 
ploughed lands of the South Downs. These echinites are 
placed by M. Desor in the genus of which an example is 
figured in Lign. 105. 
Lien. 105. Howectypus (Galerites) INFLATUS. 
Kimmeridge Clay, Switzerland. 
The left-hand figure shows the summit; the middle figure a profile; 
and the right hand, a view of the base, with the mouth in the 
centre, and the outlet towards the margin. (M. Agassiz). 
The shell is hemispherical, and circular; the base flat; 
the tubercles are disposed in series; the inside of the case is 
supported by ribs. 
DiscompEa (Galerites) castanea. Lign. 106.—The Gale- 
ritide, which have a polygonal mouth, with the tubercles 
disposed in vertical rows from the summit to the centre of 
the base, as in the Cidarites, instead of being uniformly 
spread over the surface, as in G. albo-galerus, are placed in 
the genus Discoidea, by M. Agassiz. 
A species, in which the mouth is pentagonal, and the 
