Galerites albo-galerus. _Lign. 104._--The tribe of which this genus is the type has the shell inflated, orbicular, oblong, or pentangular. The ambulacra are simple, never petaloid; the poriferous zones extend uninterruptedly from the summit to the mouth.
In the species figured _Lign. 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, 1a_); the outlet is near the posterior margin of the base. The surface of the shell is covered with granulations irregularly distributed. This species, which received the name of _albo-galerus_, from its fancied resemblance to the white conical caps of the priests of Jupiter, occurs in great numbers and perfection in the Kentish chalk; it is less common in that of Sussex. Siliceous casts of the shell are constantly found among the drift and gravel, and on the ploughed lands of chalk districts; they are popularly termed "_sugar-loaves_." The specimens obtained from the chalk, 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.
[Illustration: Lign. 104. Echinites from the Chalk. _Lewes._
1_a_.--Base of the same, with the five teeth.
[Illustration: Lign. 105. Holectypus (_Galerites_) inflatus.
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_).]
Holectypus (_Galerites_) inflatus. _Lign. 105._--In certain kinds of Galerites, the shell is strengthened internally by five strong ribs or projections, which of course leave corresponding 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_.
The shell is hemispherical, and circular; the base flat; the tubercles are disposed in series; the inside of the case is supported by ribs.