119 



M. Leske concludes with particularizing some fossil 

 echinites, which he thinks might serve to form a new genus 

 between echinanthus and spatangus ; they agreeing with 

 the former in the situation and structure of the mouth, and, 

 with the latter, in the situation of the vent. 



Le Chev. de Lamarck, to whom the lover of natural 

 history is so much indebted, afterwards proposed a con- 

 siderable change in the arrangement of these animals, and 

 in the denominations by Avhich they should be distinguished, 

 employing the form and size of the ambulacra among the 

 generic distinctions. 



The arrangement thus made was the following* : — 



DIVISION OF ECIIINIDE^. 



1. The vent below the margin, in the lower surface, or 

 in the margin. 



* The mouth beneath, always central. 

 Scutella 1 



Clypeaster > Ambulacra contracted. 



Fihularia j 



Echinonius I a u i i ^ 



Galerites ] Ambulacra complete. 



** The mouth beneath, not central, but approaching 

 to the margin. 



Ananchites. 

 Spatangus, 



2. The vent above the margin, and consequently dorsal. 



a. The vent dorsal, but approaching to the margin. 



Cassidulus. 

 Nucleoliies. 



b. The anus dorsal and vertical ; the shell regular. 



Echinus. 

 Cidarites. 



* Histoire Naturelle des Animaux sans Vertebres^ Tom. iii. p. 6, 



