118 



O. Echinus. 



Genus Genus 



1. Cidaris. 6. Echinanthus. 



2. Clipeus. 7. Echinodiscus.\\ 



3. Echinites* 8. Echinocyamus** 



4. Echinoneus.^ 9. Echinarachnius.\\ 



5. Echinocorys.\ 10. Spatangus.H 



* Klein, it may be seen, p. 116, had divided his section fibula into 

 two genera, conulus and discoide? ; but Leske seeing no material difference 

 between these two genera, included them in one under the name of echi- 

 nites; being evidently led to this from the variety of figures assumed by 

 the casts of this genus, which, from their very frequent occurrence in 

 various parts, had acquired the name of echinites vulgares ; and which in 

 many instances, have so depressed an appearance, and are so rounded at 

 their top, as hardly to possess a conical figure. These different forms 

 Klein considered as constituting merely so many varieties ; whilst 

 Phelsii'.n, regarding them as so many distinct species, gave to them 

 specific names adapted to their forms. These differences were, however, 

 considered by Leske, as dependent on compression, which he supposed 

 might have taken place during the process of petrifaction, and therefore 

 he could not so separate them. 



Another circumstance requires to be taken into consideration: In 

 numerous specimens that have not suffered mutilation by fracture, it 

 appears that this form has proceeded from a deficiency of the infiltrated 

 siliceous matter of which the casts have been formed. Many of them 

 have evidently been subjected to this infiltration whilst placed in their 

 natural situation, on their base, and hence have been filled chiefly from 

 below upwards ; and, consequently, if from any circumstance the infil- 

 tration ceased before the mould had been filled, the more pointed upper 

 part would be wanting, and the remaining part would be nearly level or 

 rounded on its upper surface. Others, indeed, possessed originally a 

 compressed discoidal figure; but these, as well as those which have been 

 just described, are considered by Leske as properly referrible to conulus. 

 No reason is offered by this attentive observer, nor does any appear, for 

 their being placed under a genus bearing another name. 



t This genus was formed by Phelsum, and agrees, as is observed by 

 Leske, with the discoides of Klein, except in the periphery being ovate, 

 or oval rounded, and never angular, and the vent being oblong and 

 nearer to the mouth. 



J In this genus he includes the two genera galea and galeola of Klein. 



Includes all the scutiform echini of Klein, whether ovate or angular. 



|| Is substituted for the placenta of Klein it had been previously 

 adopted by Breyn. 



** This is a new genus formed by Phelsum, the generic characters 

 of which are nuciform ; ten stelliform, biporous, ambulacra ; the mouth 

 and vent near to each other, about the centre of the base. 



ft This agrees with arachnoides of Klein, the name only being 

 changed. 



tt The sections of Klein, cor marinum, divided into the genera spa- 

 tangus and spatagoides, and the section ovum marinum divided into brissus 

 and brissoides, were, after much consideration, included by Leske in this 

 genus spatangus ; he separating the members of this genus into four 

 families. I. Cordated spatangi, with a sulcated vertex. 2. Cordated 

 spatangi, not sulcated. 3. Brissi, oval spatangi, the ambulacra sulcated. 

 4. Brissoides, oval spatangi, the ambulacra not sulcated. 



