ECHINUS. ECHINODERMATA. 399 



on which are articulated moveable and caducous spines ; 

 five compartments, each margined with two multiporous di- 

 verging bands, which extend in rays from the summit to the 

 mouth ; mouth inferior, central, armed with five bony ena- 

 melled pieces ; anus superior. 



The animals of this genus, like the preceding, move by means of their spines and 

 tentacula. The body is covered with a calcareous crust composed of angular por- 

 tions joined together, and pierced with regular rows of small holes for the pas- 

 sage of the tentacula or membranous feet. The mouth is furnished with five teeth 

 or bony plates set in a calcareous and complicated frame furnished with muscles 

 and suspended in the large opening of the shell. The intestine is very long and 

 attached in a spiral form to the interior walls. A double vascular system runs 

 along this canal ; and five ovaries placed around the anus have each a particular ori- 

 fice. These form the edible part of the animal. The Echini feed on small shells. 

 Their movements are slow. The interior of the shell is always full of water. Many 

 fossil species of this and the preceding genus are found in the chalk formation, gene- 

 rally filled with silex. 



* Shell orbicular. 

 E. esculentus, Lin. Shell hemispherical-globose, with porous bands, 



obsoletely verrucose ; spines short, violet coloured. 4 inches in 



diameter. Coasts of Europe, &c. B. Penn. Brit. Zool. iv. pi. 36, 



fig. 1. 



E. granularis, Lam. Shell hemispherical, depressed, granulated 

 and rough ; bands porous, verrucose, and irregular; base flattish. 

 Lam. iii. 44. 



E. lividus, Lam. Shell hemispherical, depressed, the bands porose, 

 flexuous, subverrucose ; spines sharp, long, striated, livid fuscous. 

 Inhabits coasts of the Mediterranean. Lam. iii. 50. 



** Shell oval or elliptical. 



E. atratus, Lin. Shell hemispherical-oval, depressed, blackish vio- 

 let, spines of the back imbricated, very short and obtuse. Inha- 

 bits Indian Ocean Lam. iii. 51. 



E. trigonarius, Lam. Shell hemispherical-oval, with porose and 

 flexuous bands ; tubercles mammillated ; spines long, trigonal, at- 

 tenuated and obtuse. Lam. iii. 51. 



Gen. 7. NUCLEOLITES, Lam. 



Body oval or cordiform, slightly irregular, convex ; compart- 

 ments complete, radiating from the summit to the base ; mouth 

 subcentral ; anus above the margin. 



The species of this genus are fossil. 



Gen. 8. CASSIDULUS, Lam. 



Body irregular, elliptical, oval or subcordiform, convex or gib- 

 bous, furnished with small spines; five stellated compartments; 

 mouth subcentral ; anus above the margin. 



C. Australis, Lam. Obovate, widest behind ; spines small ; subca- 

 rinated round the vertex ; anus transverse ovate. Inhabits seas 

 of New Holland Lam. iii. 35. 



The other species of this genus are fossil. 



