ECHINODERMATA. 155 
fig. 28. Ananch. hemispherica Cuv. and Bronen. 1.1. fig. 8, &c. All the 
species of this genus are fossil and belong to the chalk-formation. The 
casts of the internal cavity in Fire-stone (nucleus, moule intérieure) shew 
minute elevated points in place of the ambulacral pores ; such a moule is 
the Ananchytes pustulosa LAM. 
Dysaster AGAss. (Collyrites DESMOUL. in part, species of Spa- 
tangus and Ananchytes Auctor.) Test rotund or cordate, with 
ambulacra not interrupted, mouth sometimes almost central not 
transverse. Ambulacra above radiating from a double vertex, the 
three anterior confluent in the central part of the test above, the 
posterior ones above the anus. 
Sp. Dynaster carinatus, Spatangus carinatus Bronn Leth. géogn. Tab. Xv1t. 
fig. 7, in the Jura-formation like most of the species of this genus. Comp. 
Desor in the 3d number of Acassiz Monogr. d’ Echinoderm., who describes 
20 species, of which 17 are from the Jura-formation and 3 from the chalk- 
period. No species either of this genus or of Ananchytes has been 
discovered belonging to the present animal world; AGassiz places this 
genus in the following division, that of the Clypeustroidea; its place cannot 
be determined with precision, before it is known whether teeth be present ; 
still we are of opinion that it ought not to be separated from Ananchytes, 
but forms the transition between that genus and the following division. 
b) Mouth central or sub-central.  (Clypeastroidea AGASs.) 
Spines little evolved, sometimes very small, resembling hairs. 
Galerites LAM. Body conoid or sub-oval, plane beneath. Am- 
bulacra in ten furrows in pairs from the vertex to the base, radiately 
inscribed, not interrupted. Anus in the margin, or beneath and 
near the margin. Genital pores four. 
Genera: Clypeus Kintn, Acassiz, Discoidea Kunin, AGAssiz, 
Galerites AGASS. 
Sp. Galerites albo-galerus Lam., Cuv. R. Ani,, édit. ill. Zooph. Pl. xiv. fig. 4, 
Bronn Leth. géogn. Tab. xxix. fig. 18, Acass. Monogr. 3° Livr. Tab. t. 
f. 4—11, Tab, x1. f. 7, &c. This genus consists of fossil species of the 
Jura and especially of the chalk-period. Comp. on this and some other 
genera Drsor in the 3d number of Acassiz Monographies d’ Echinod. 
already referred to. 
Pygaster AGAss. Body depressed, with outline orbicular or 
sub-angular, beneath concave. Anus large, superior, situated in 
a broad furrow. Genital pores four. 
All the species of this genus are fossil; most of them belong to the 
Jura-formation. 
