342 ECHINOBRISSUS 



Test orbicular ; upper surface irregularly convex and depressed ; sides tumid ; apical 

 disc complex and central ; ambulacral areas lanceolate ; poriferous zones narrowly petaloid 

 between the border and disc ; posterior lobes obsolete ; anal valley broad, extending from 

 the disc to the border ; vent large, situated in the upper part, near the disc ; base flat or 

 slightly concave ; mouth sub-central, situated in a depression nearer the anterior border. 



Dimensions. — Height, eight tenths of an inch ; transverse diameter, one inch and six 

 tenths ; antero-posterior diameter, one inch and six tenths. 



Description. — The tumid sides, obsolete lobes, orbicular circumference, its length and 

 breadth being equal, with the broad, flat, and somewhat irregular dorsal surface, serve to 

 distinguish this species from its congeners. 



The ambulacral areas are narrow, and nearly all of the same width (fig. 2 a) ; they have 

 a more petaloidal form than in the preceding species, and are furnished with two rows of 

 small tubercles arranged in zig-zag lines on the areas, the external row being the largest 

 and most regular (fig. 2 e), whilst the middle of the area is covered only with minute 

 granules. 



The poriferous zones are moderately wide, and with the ambulacral areas form well- 

 developed petaloidal figures on the upper surface of the test ; the pores of the inner row 

 are round, those of the external row are oblong (fig. 2 e) ; there are about six pairs of 

 holes opposite each inter- ambulacral plate ; on the upper surface the pores are wider 

 apart (fig. 2 ^), on the sides they are close together (fig. 2 c), at the margin they are very 

 indistinct (fig. 2/), at the base they are scarcely visible and still more widely apart, and 

 continue so to the peristome (fig. 2 5). 



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

 narrowest, the postero-lateral are wider, and the single area is the widest (fig. 2 a, d) ; 

 the sides are more or less tumid (fig. 2 c), and the upper surface is irregularly convex (fig. 2/), 

 in consequence of the antero- and postero-lateral areas being slightly depressed in the 

 centre (fig. 2 c,f); the inter-ambulacral plates form long pentagons, bent upwards in the 

 middle (fig. 2 e). Each plate is covered with about twenty very small tubei^cles, arranged 

 in three rows ; in a large majority of specimens they are so minute on the sides, margin, 

 and upper surface that it requires the aid of a good lens to discover them, at the base they 

 are larger and crowded closer together ; each tubercle is surrounded by a sunken areola 

 (fig. 2 e), and the inter-tubercular surface of the plates is closely crowded with microscopic 

 granules which encircle the areolas or fill up all the intervening spaces. The single inter- 

 ambulacrum is not at all produced, and the lobes are very small. The anal valley is large ; 

 it commences at the posterior border of the disc and extends to the margin (fig. 2 a. j/). 

 The large vent has an elliptical shape, and opens near the surface in the upper third of the 

 valley, whilst the lower two thirds of that depression form a considerable furrow in the 

 middle of the area (fig. 2 a, ff). 



