from the Island of Malta. 75 



of Westphalia, where it appears to be common. The specimen 

 before us is the only one we know from Malta. The circum- 

 ference is nearly ovato-orbicular, slightly inclining to an obsolete 

 pentagon, with the posterior border most produced. The dorsal 

 surface is highly convex, the posterior half being much more so 

 than the anterior. The ambulacral areas are unequal, as regards 

 l( -Mirth, width and development; the single anterior area is the 

 shortest and narrowest, the antero- laterals are next in size, and 

 the postero-laterals are the most fully developed ; they have all 

 a lanceolate form, with blunt apices. The surface of the areas 

 is on a level with that of the interambulacra, in the specimen 

 before us; but in some of the Westphalian Urchins the ambu- 

 lacra! areas form convex projections on the surface of the test. 

 The poriferous avenues, extending down more than two-thirds of 

 the dorsal surface, are well marked in our specimen, and lie in 

 depressions of the test ; they consist of two series of pores ; the 

 internal holes are round, the external run into oblique slits that 

 have a direction upwards and inwards ; the pores on the right 

 and left sides of the areas do not always correspond in length ; 

 thus, the anterior pores in the antero-lateral areas are often only 

 half as long as those on the posterior side of the same areas, 

 and we see a similar inequality, although not to the same 

 extent, in those of the single ambulacrum. The anterior and 

 posterior pair of the interambulacral areas are much alike in 

 form and development ; but the single interambulacrum is 

 different, it forms a more convex eminence than the others 

 above, and is produced into a slight caudal appendage behind. 

 The apical disc is small and excentral, situated nearer the an- 

 terior border. The madreporiform body occupies the centre, 

 around which the four genital holes are pierced. The base is 

 concave ; the mouth is nearer the anterior border, is transversely 

 oblong, and surrounded by five lobes, formed by the termination 

 of the interambulacra ; the posterior single lobe is the largest ; 

 the anterior pair are next it in size, and the lobes of the postero- 

 lateral areas are the smallest and most contracted. Between 

 the five oral lobes, the poriferous terminations of the ambulacral 

 areas form petaloidal depressions, which are perforated with 

 numerous holes ; these run out and form lines which indicate 

 the basal boundaries of the areas. The anus is transversely 

 oval, y^jths of an inch in its long diameter, is more convex on 

 its anterior than its posterior border, and is situated close to the 

 margin; it is rather larger than the mouth-opening. The 

 tubercles are small, uniform in size, and closely set together on 

 the dorsal surface, and longer and more widely apart on the base. 

 Affinities and differences. The great convexity of the dorsal 



