PIPER. 



147 



the dental apparatus, which resembles that of the Echinus. 

 The surface is covered with spines, which are of two sorts ; 

 the one kind few in number, and very long, measuring an 

 inch and a half in length, sometimes more. These are 

 slightly of a clavate form, and furrowed with about ten 

 deep striae, which are as broad as the intervening crenated 

 ridges. The prominences round their bases are finely 

 striated, and not furrowed by the stria? of the rest of the 

 spine. The spines of the second sort are very short, flat- 

 tened, and finely striate. When the spines are rubbed 

 away, we then see the wide inter-ambulacra! spaces, each 

 bearing about ten large tubercles, placed in the centre of 

 wide, smooth, circular depressions, which are bordered by 

 a frame of small tubercles, and separated from each other 

 by transversely striated spaces. The large tubercles some- 

 what resemble the Urchin itself in form, and are smooth 

 and polished, with a depression or perforation in their 

 centres, which, however, does not run through the sub- 

 stance. This character is common to the genera Cidaris 

 and Diadema. The inter-ambulacral spaces are extremely 

 narrow, and equal in breadth throughout ; they bear four 

 longitudinal rows of minute tubercles or granules, and are 

 waved in consequence of the undulations of the avenues, 

 each of which is composed of a longitudinal row of pores 

 arranged in pairs. A furrow connects the pores of each 

 pair. All the long spines are placed on the large inter- 

 ambulacral tubercles, one of which is seen on each inter- 

 ambulacral plate. The depression on the summit of the 

 tubercle is for the reception of the ligament of the spine. 

 All the smaller spines are placed on the granules forming 

 radiated borders round the tubercles, the avenues, the 

 anus, and the mouth. 



This beautiful Urchin was first recorded as British, and 



i2 



