426 Mr. Gray on the Sea Eggs, [Dec. 



more or less distinct grooves, situated at the base of each arm 

 of the internal processes, and diverging from them ; and on the 

 edge of the extra ambulacral beds just by the outer margin of 

 the ambulacra. I am not quite sure what is the use of these 

 grooves, but they have very much the appearance of pulleys, 

 over which some muscles work, and examining a specimen of 

 Echinus mammil/aiuspYeservedins^'mis, I observed ten shrub-like 

 bodies attached to filiform nerves, or muscles, which appear to 

 extend up towards the body of the shell : I am, therefore, 

 inclined to think that they are the means by which spines are 

 moved and nourished^ but I cannot at present decide, from the 

 want of live and preserved specimens, to dissect and examine 

 more minutely. 



This group is synonimous with the genus Echinometra of 

 Bryerius, and the section Cidaris of Klein. It is divisible into 

 two families. 



Jam. 1. CiDARiD^. Cidaris, Lam. 



Body with two-sized spines ; larger ones club-shaped, or very 

 long ; spine-bearing tubercles perforated at the apex. 



Gen, I. CiDARis, Klein, Lam. Turbans. 



Body depressed, spheroidal ; ambulacra waved ; small spines 

 compressed, two edged, two rowed, covering the ambulacra, and 

 surrounding the base of the larger spines. 



This genus may be divided according to the form of the larger 

 spines ; the extra ambulacral beads have only. two rows of spines. 



C. imperiaUs, Lam. Klein, t. vii. f. A. 



2. DiADEMA. Diadems. 



Body orbicular, rather depressed ; ambulacra strait, spines 

 often fistulous. 



*D. setosa, Leske, Klein, t 37, f. 1, 2. Echinus Diadema, 

 Lin, **D. calamaria. Echinus, Pallas, Spix, ZooL t. 2, f. 4, 8. 



3. ASTROPYGA. 



Body orbicular, very depressed ; ambulacra strait ; ovarian 

 scales very long, lanceolate ; beds with several series of spines. 

 A. radiata, Leske, t. 44, f. 1. 



Fam.2. Echinid^, 



Body with nearly uniform spines ; spine-bearing tubercles not 

 perforated. 



Echinus, Lin. Van. Phelsum. 



Body orbicular, subangular; beds with cross rows of spines. 



E. esculentus, Lin. 



Echinometra, Bryerius. Van Phelsum. 

 Body ovate or elliptical, each bed with two rows of large 

 tubercles j ambulacra flexuous ; allied to Cidaris, 



