ECHINODERMATA. 153 



fig. ?.8. Ananch. hemisphcerica Cuv. and BRONGN. 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 interieure) shew 

 minute elevated points in place of the ambulacral pores ; such a moule is 

 the Ananchytes pustulosa LAM. 



Disaster 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. geogn. Tab. xvn. 

 fig. 7, in the Jura-formation like most of the species of this genus. Comp. 

 DESOR in the 3d number of AGASSIZ Monogr. d'Echinoderm,., who describes 

 20 species, of which 1 7 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 Clypeastro'idea ; 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. 



6) Mouth central or sub-central. (Clypeastro'idea 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 KLEIN, AGASSIZ, Disco'idea KLEIN, AGASSIZ, 

 Galerites AGASS. 



Sp. Galerites albo-galerus LAM., Cuv. R. Ani., edit. til. Zoopk. PI. xrv. fig. 4, 

 BRONN Leth. geogn. Tab. xxix. fig. 18, AGASS. Monogr. 3 e Livr. Tab. r. 

 f. 4 n, Tab. xiii. 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 DESOR in the 3d number of AGASSIZ 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 . 



