OF WESTERN SINI). 207 



lateral nearly as long as the posterior ; the pores large, rather closely placed ; poriferous 

 zones costulate, a little broader in the lateral than in the posterior petals, and with 

 their interporiferous area narrower ; some small isolated tubercles on the margins of 

 the ambulacra ; the peripetalous fasciole subpentagonal, scarcely sinuous, touching the 

 extremity of the petals. Lateral interambulacral areas a little broader than the 

 anterior and the posterior, all a little prominent in the neighbourhood of the summit. 

 Anus marginal ; periproct rounded 1 Inferior disk almost flat, very feebly inflated in 

 front of the anus ; mouth situated at the anterior two fifths of the major axis ; peristome 

 transversely elongate and strongly labiate, surrounded with a distinct floscelle of 

 ambulacral pores, simple for the most part. On the abactinal surface some large 

 granules may be seen, and those on the actinal interambulacral areas are still larger. 

 The largest individual observed M'as 3^ centimetres in length, a little more than 3 centi- 

 metres broad, and a little less than 2 centimetres high. A flatter variety was only 

 1 centimetre in height and 2-g- centimetres long. 



To this description we may add that a large, complete, and well-developed subanal 

 fasciole is present, of wide extent, and circumscribing a subreniform area on the 

 rounded margin, which joins the actinal surface and the posterior extremity. The 

 course of this fasciole beneath the periproct is deeply reentering, and the opposite part 

 of the fasciole where it passes the hindermost part of the actinal plastron is more or 

 less incurved, which causes the fasciole to approach somewhat the outline of the 

 figure 8- About five or six pairs of minute pores are present on either side of the 

 subanal plastron within the fasciole. The course of the peripetalous fasciole is not 

 correctly shown in d'Archiac and Haime's drawing (op. cit. plate xv, fig. 7); a 

 slight but abrupt bend being present both in the lateral and the anterior interradia 

 (although one or both of these may frequently be absent on either side), and the fasciole 

 does not pass forwards over the margin, as the figure would lead one to suppose. The 

 larger primary tubercles which are present on the interradia within the peripetalous 

 fasciole are not regularly disposed along the margins of the grooves of the petaloid 

 ambulacra as represented in the figure and the description ; they have a much more 

 distributed appearance, and sometimes two or three are together in irregular horizontal 

 series. On either side of the groove of the odd anterior ambulacrum each plate has a 

 wedge-shaped group of larger tubercles, the largest being nearest to the groove, and 

 those external to them becoming gradually smaller. On the actinal and anal plastrons 

 the ornamentation diminishes in size towards the slightly prominent culminating point 

 at the posterior extremity of the actinal plastron ; and the tubercles are arranged in 

 lines, more or less distinctly traceable, which radiate from this point. 



There are a number of young specimens in the collection, which accord in all 

 particulars with the adult form ; the smallest, which measures 17 millim. in length, 

 is figured in Plate XXXV. 



BemarJcs. The generic diagnosis given above sufliciently indicates the grounds on 

 which we have removed this species from the genus Brissopsis, in which it was originally 

 placed by dArchiac and Haime. The shape of the test, with the upper surface 

 arching direct from the margin (which, though rounded, is thin and not tumid), together 



2e2 



