MEOMA VENTRICOSA. 359 



anterior extremity to apex, lateral ambulacra deeply sunken, posterior pair 

 somewhat longer than anterior pair, which diverges at a much greater angle 

 from the scarcely marked odd anterior ambulacrum ; this is placed in a very 

 slightly marked anterior groove. Peripetalous fasciole of uniform breadth, well 

 defined, four genital openings diverging posteriorly. On the interambulacral 

 plates, enclosed by the fasciole, the tubercles are arranged in single rows paral- 

 lel to the suture ; the rest of the test is covered by closely packed, uniform- 

 sized tubercles, carrying short, sharp spines. The tubercles of the actinal part 

 of the test are larger immediately adjoining the ambulacra, diminishing 

 in size towards the edge and towards the central part of the actinal plas- 

 tron. This plastron is bottle-shaped, short-necked, near the actinostome, 

 with a very indistinct keel near the central portion, bounded posteriorly by 

 the narrow, usually open, subanal fasciole, the anal extremity of which is 

 bent near the base of the anal system. The actinostome is deeply sunken, 

 the posterior lip extremely prominent and projecting almost as far as the 

 anterior edge of the actinostome. The anal system is small, elliptical, cov- 

 ered by irregular polygonal plates carrying spines, diminishing rapidly in 

 size towards the anal opening. The edge of the interambulacra adjoining 

 the ambulacral plates of the lower side, the space round the anal system and 

 round the actinostome, is closely crowded with two kinds of pedicellarire, one 

 with short head, broad base, and short arms, the other with long triangular 

 arms. Both are carried upon moderately long, stout stems. 



A small specimen of Meoma, not measuring quite an inch in length, which 

 D'Orbigny had described as Schizaster cubensis, showed no special points 

 of difference from the adult. 



Liitken first referred this species to the genus Meoma of Gray, established 

 for a presumed Australian species, M. grandis. Liitken also, in 1863, called 

 my attention to the generic identity of Kleinia nigra, A. Ag., with Meoma, 

 which I had with doubt referred to Kleinia. This mistake I was led into 

 by the fact that Gray himself did not refer Brissus ventricosus to Meoma, 

 but still retained it in a section of Brissus. This shows how little value 

 the subdivisions which Gray so frequently introduces in his genera of Echini 

 must have (often copied without any attempt at a more accurate discrimina- 

 tion of the species from similar headings in the Catalogue Raisonne), when 

 two species as closely allied as Meoma ventricosa and Meoma grandis are 

 placed in two genera ; or when in the subdivisions of Echinocardium, as another 

 instance, Echinocardium ovatum is placed in the subdivision of the genus 



