]SS COTTALDIA. 



forming distinct liorizontal rows on the plates of the inter-ambnlacra, and having the 

 pores unigeminal throughout the narrow areas. 



The test varies in form in different individuals from nearly a globular shape, as in PL 

 XLV, fig. 1, to forms more or less depressed at both poles, as in figs. 2 and 3. The 

 uniformity in size and arrangement of the numerous small tubercles covering the surface, 

 and the division of the same into five broad and five narrow segments (fig. 1 d), by 

 the poriferous zones radiating from the circumference of the apical disc (fig. 1 h) and 

 converging below around the peristome (fig. 1 c), impart a remarkable physiognomy to- 

 this pretty little Urchin ; the medial suture down the middle of the inter-ambulacra is 

 often depressed, and then Cotfaldia Beneitia resembles a little melon, having its surface 

 divided into fifteen lobes (fig. 1 b, d). 



The ambulacral areas are about one third the width of the inter-ambulacral, and at 

 the ambitus there are three or four tubercles on each plate (fig. 2 h), with numerous small 

 granules around them ; the outer rows of tubercles are the most persistent, and the inner 

 rows in general are limited to the ambital region of the test ; the poriferous zones are very 

 narrow, and the pores numerous and unigeminal throughout (fig. 2 h) ; near the base 

 they show a disposition to fall into triple oblique pairs, as in the genus Echinus, but the 

 deviation is so slight that it is only occasionally seen in exceptional specimens ; there 

 are in general three pairs of holes opposite each ambulacral plate (fig. 1 e and fig. 2 b), 

 so that in the specimen I am describing there are quite 100 pairs of holes in each zone. 



The inter-ambulacral areas are three times as wide as the ambulacral ; the plates are 

 very narrow in proportion to their length, and in the specimen before me there are thirty- 

 five plates in each column ; each plate has a horizontal series of small equal-sized spini- 

 ferous tubercles ; in the longest plates at the ambitus there are from nine to eleven on 

 each according to the age and size of the specimen under examination ; the tubercles of 

 both areas are of the same size, but they are rather more closely set together, and more 

 obliquely placed in consequence in the ambulacral areas (see fig. 1 e and fig. 2 b) ; the 

 number of tubercles in each vertical row varies with the age and size of the specimen ; 

 they are most numerous near the ambital region ; the rows nearest the poriferous zones 

 are the longest and most persistent, and those near the miliary zone the shortest and most 

 frequently absent. In some large specimens there is a depression in the line of the 

 median suture in the inter-ambulacral areas, which gives this space a bilobed appear- 

 ance; as these areas are nearly half the width of the ambulacral, the whole circum- 

 ference of the test is divided by the five sutural depressions into ten poriferous zones 

 and fifteen well-marked lobes, as represented in fig. 1 a, b, c, d, and this imparts a 

 remarkable symmetrical neatness to the physiognomy of the Urchin. 



The mouth-opening is nearly circular, and about one half the diameter of the test (fig. 

 1 c) ; the peristome, which is superficial, is very feebly notched opposite the zones. 



The apical disc is a small ring-like structiu'e slightly projecting from the surface of 

 the test (fig. 1 b) ; the ovarial plates are sub-triangular (fig. 1 b), and perforated near 



