ECHINUS. 135 



posed entirely of spines, extends from the mouth down to a transverse 

 elliptical arrangement, the shelly portion, constituting the ellipse, being 

 quite smooth. This transverse arrangement sometimes resembles a deep 

 cleft in the shell, but here there is none. 



Much difference in the perfection and number of the pores, and of the 

 various superficial figures and appearance, distinguishes different shells. 



The substance of all is very brittle, thin, and light, compared with 

 their dimensions. 



This animal is usually sunk amidst the sand, of which it swallows an 

 extraordmary quantity, so that its weight becomes surprising and un- 

 natural. Comminuted shells, of various species, are mixed with the sand, 

 but their inmates do not appear to have been rendered prey. No speci- 

 men has fed on any substance offered to it in captivity. 



Professor Delle Chinie gives dissections of this subject. 



Plate XXXII. 



Fig. 12. Spatangus purptireus, reduced, under surface. 

 13, 14. Suckers enlarged. 



15. Shell divested of the spines, shewing the stellate figure on the 



convex or upper side. 



16. Shell divested of the spines, shewing the site and fissure of the 



mouth, under surface. 



§ 3. Spatangus (Flavescens), — niveus. — Plate XXXIII. figs. 1, 2, 3, 4, 

 5, 6, 7, 8, 9. 



This is a fine and dehcate looking animal, somewhat heart-shaped 

 like the preceding, liut thicker in proportion, and the parts more pro- 

 minent or rounded. 



The largest specimens falling into my possession, extended two 

 inches and a half in length. Others were about an inch and a half, 

 nearly two inches broad, and one in thickness. Such dimensions are to 

 be understood as of animals invested with the white or yeUow spines, 

 wherewith they are totally covered. 



