174 PEDINA. 



variety of Pedina sublevis ; that name having thus become obsolete, so far as it relates to 

 the Swiss urchin, and our species having been beautifully figured, in the ' Memoirs of the 

 Geological Survey,' under the specific name I first gave it, I have retained it in this 

 work. 



The test of this urchin is in general circular, but in some specimens it has a sub-pen- 

 tagonal form (fig. 1 b). Its sides are always more or less tumid, and it is nearly equally 

 depressed on the upper and under surfaces (fig. 1 c). 



The narrow ambulacral areas are furnished with two rows of small, numerous, equal- 

 sized tubercles, from twenty-five to thirty in each row, which are closely set together 

 on the margins of the area, and arranged with great regularity throughout ; in the 

 middle third there are two rows of minute tubercles within the marginal rows, which 

 disappear above and below ; a double line of small granules descends in a zigzag form 

 between the tubercles, and sends small lateral branches, to encircle the marginal rows 

 (fig. 1 a, b, e). 



The inter-ambulacral areas are four times as wide as the ambulacral (fig. 1 c) ; in the 

 specimen figured there are fifteen plates in each column ; each plate supports one 

 primary tubercle, situated near the zonal border of the plate (fig. 1 e), and between 

 the peristome and the circumference, two secondary tubercles, on the sutural side of the 

 primaries (fig. 1 e) ; on the upper surface the secondary tubercles gradually disappear, so 

 that the under surface of the test (fig. 1 a) is much more tuberculous than its upper 

 surface (fig. 1 b) ; the areolas are very narrow, but not at all excavated, and around them 

 circles of small granules are regularly disposed ; the primary tubercles form ten con- 

 spicuous rows, which are nearly equidistant from each other, whilst the secondary tubercles 

 are not so regular in their arrangement. 



The poriferous zones are wide, in which the holes are closely arranged in triple oblique 

 pairs ; the obliquity, however, is greater on the upper than on the under surface, where 

 the holes are so disposed, that the undermost pair of each trigeminal rank forms an oblique 

 line with the uppermost pair of the rank immediately below it, leaving the middle pair 



by themselves, thus — ":. ... Each pair is surrounded by a slight oval rim, which is 



only seen, however, on the best-preserved specimens ; there are three oblique pairs of holes 

 opposite each large plate (fig. 1 c) ; and between each trigeminal rank there are two small 

 tubercles (fig. 1 b). 



The base is flat, the mouth opening small, being about two sevenths the diameter 

 of the test ; the peristome is decagonal (fig. 1 a), and divided by deep notches into ten 

 nearly equal-sized lobes, those corresponding to the ambulacra are the largest. 



The apical disc is moderately large, being two sevenths the diameter of the test 

 (fig. 1 b) ; it is often well preserved, as in fig. 1 b ; the genital plates are nearly all of 

 the same size (fig. 1 d) ; the right antero-lateral, supporting the fine spongy madreporiform 

 body, is a little larger than the others (fig. 1 d) ; they have all a heptagonal shape, and 



