464 PLEURECHINUS. 



tubercles are but slightly smaller than the interambulacral tubercles at the 

 ambitus, and diminish very gradually in size towards the abactinal pole. 

 The median amhulacral space is occupied by two vertical rows of discon- 

 nected tubercles of very unequal size, the one being as large nearly as the 

 primaries near the ambitus, but rapidly decreasing in size, while the other 

 is made up of minute secondaries. At the base of the primaries there are, 

 towards the median side, a few very small secondaries. On the actinal side 

 of the ambulacra, as in the interambulacral region, the pits become very 

 small, the tubercles of uniform size, with irregular horizontal lines of 

 small secondaries along the sutures of the plates. The poriferous zone is 

 broad, with minute secondaries at the extremity of the ridges separating 

 the pores, and on the outer edge of the zone a vertical row of somewhat 

 larger tubercles. Auricles are high, thin, with high connecting ridge and 

 minute foramen. 



The spines are long, quite flattened, of a pink color, with three or four 

 purplish transverse bands. Actinal membrane bare; the ten buccal plates 

 prominent, though not large. Actinostome small, scarcely indented, some- 

 what sunken. The test of dried specimens is usually of a uniform drab color. 



No. <'f 

 Spine. Plate. 



23. 



11.8 



East Indian Ocean ; China. 



(TEMNOPLEURUS.) Pleurechinus. 



Fleurechinus Agass., 1841, Mon. Scut. 



Echini resembling Temnopleurus, but more ovoid outline, with simple 

 pores arranged in straight or slightly undulating lines. Actinostome small, 

 scarcely cut. Tubercles imperforate, indistinctly crenulated. The sutural 

 impressions in the shape of deep disconnected pits, occurring not only in 

 the angles of the plates, but sometimes three or four, even six, in a horizontal 

 suture. 



