from the Island of Malta. 85 



slightly flattened at the cheeks, bulging out at the sides, and 

 from thence tapering abruptly towards the posterior border, 

 where it is truncated obliquely downwards and forwards; the 

 anterior part of the test is flattened and depressed, and the pos- 

 terior portion much elevated, from the circumstance of the single 

 interambulacrum forming two prominent ridges, one on the 

 dorsal, and the other on the basal surface, which gives increased 

 depth to the test, tilts it up, and forms an inclined plane of the 

 dorsal surface. The petaloidal ambulacra are short, broad and 

 leaf-like ; the anterior pair are slightly flexed forwards and form 

 an angle of about 15 ; their anterior poriferous zone is nearly 

 as complete as the posterior zone, which contain respectively 

 sixteen and eighteen pairs of pores ; the posterior pair form two 

 oval leaflets, the bases and apices of which are nearly equally 

 curved, and closed with pores, having about eighteen pairs of 

 pores in each zone ; they describe an angle of about 60. The 

 single anterior ambulacrum makes a very slight depression on 

 the upper part of the anterior region, and the anteal sulcus 

 formed by it is inconsiderable when compared with other con- 

 generic forms ; the anterior and lateral pairs of interambulacra 

 carry a few large crenulated and perforated tubercles on the 

 upper part of their dorsal surface ; on the anterior pair there are 

 from seven to eight, and on the posterior pair from four to five 

 of these tubercles, which are neither so large nor yet have such 

 deep areolas as their homologues in S. Hoffmanni. The single 

 posterior interambulacrum is narrow, but greatly developed in 

 the vertical diameter ; above, a blunt prominent ridge commences 

 near the apical disc and extends to the posterior border ; below, 

 another ridge commences a short distance from the truncated 

 portion of the border, and extends to the centre of the mouth ; 

 the base is slightly convex from side to side, besides being 

 raised in the middle of its posterior part by the ridge just 

 alluded to. The tubercles on the basal portions of the anterior 

 and posterior interambulacra are not very large, but are disposed 

 with great regularity ; those on the ridge-like prominence of the 

 single interambulacrum are arranged in lines which radiate in 

 all directions from a point ; those on the pairs gradually decrease 

 in size from the mouth to the border ; between these two groups 

 of tubercles there is on each side a smooth track, corresponding 

 with the course of the postero-lateral ambulacra from the border 

 to the mouth : the anus is large and circular, and occupies the 

 upper part of the posterior border ; the subanal fasciole is de- 

 nuded ; the mouth is likewise large and transversely oval, and is 

 situated near the anteal sulcus. The apical disc is excentral, 

 being situated about the anterior part of the middle third of the 

 test ; it is small, and is perforated with four genital holes. The 



