398 PYGUEUS 



the upper surface is very much depressed, and remarkable for the costated character of 

 the ambulacra! areas, which are widely petalloid four fifths of the distance between the 

 disc and border (fig. 1 a). The poriferous zones consist of an inner row of oblong 

 pores, and an outer row of oblique, slit-like pores, conjugate throughout by fine sulci 

 (fig. 1 dt) ; the transverse pores are separated by thin septa, on the surface of which a series 

 of minute granules are arranged ; there are from seven to nine pair of pores opposite 

 each large inter-ambulacral plate (fig. 1 d). Near the border the pores are simple, and set 

 close together ; they continue so round the marginal fold ; at the base they are placed wide 

 apart, from their ambulacra! plates being large and rhomboidal ; on the outer two thirds of 

 these segments, near the mouth, the areas suddenly expand (fig. 1 h), and between the oral 

 lobes they again as suddenly contract, forming thereby spoon-shaped depressions around 

 the mouth (fig. I e). On the sides of these depressions the poriferous zones present a 

 remarkable development (fig. 1 e) ; the pores form three crescentic rows on each side of 

 the depression, between the single pair and the marginal contraction (fig. 1 e). The 

 lobes are very large and mammillated, and form considerable eminences around the mouth, 

 their lip-like forms extending over the border of the peristome (fig. 1 /). 



The inter-ambulacral areas are of unequal width ; the antero-lateral pair are the narrowest, 

 the single posterior rostrated area the widest, and the postero-lateral pair of intermediate 

 dimensions; their upper surface is almost uniformly sloped, and their basal portions 

 extremely flat; in most Pyguri the prominence of the inter-ambulacral cushions might 

 be considered a generic character; in this species, however, the convexity of these 

 basal segments is very inconsiderable (fig. 1 c). 



The mouth-opening is large and sub-central, nearer the anterior border ; the peristome 

 is pentagonal, and surrounded by five mammillated prominent lobes, which project, with 

 lip-like processes^ over the oral opening (fig, 1 b, f) ; between the lobes the ambulacra are 

 much contracted, and beyond the lobes they form wide phylloidal expansions, on the sides 

 of which the poriferous zones consist of three concentric rows of holes (fig. 1 e) ; the struc- 

 ture of the oral lobes, phylloidal ambulacra, and trigeminal pores, form the most remarkable 

 features in this disciform species. 



The apical disc is small and sub-central, it forms the vertex of the test (fig. 1 c), 

 and the centre of a conoidal elevation, occasioned by the costated character of the am- 

 bulacral areas ; the disc consists of fom' small perforated genital, a single imperforate 

 genital, and five very small ocular, plates ; the small madreporiform body rises from the 

 surface of the right antero-lateral genital, covers the surface of the other plates, and forms 

 a. round spongy prominence in the centre of the disc (fig. 1 a). 



The dorsal tubercles are very small, and arranged in four or five rows on each plate ; 

 they are surrounded by well-defined sunken areolas, and all the intermediate surface is 

 occupied by microscopic miliary granules, which are likewise encircled by sunken areolas ; 

 when viewed with an inch object-glass, the plates are seen to possess a delicately sculptured 

 surface (fig. 1 a) ; the basal tubercles on the sides of the inter-ambulacra, and the convex part 



