SCHIZASTER. 163 



between irregularly hexagonal plates, in double series, from the apex 

 to the mouth. The ambulacral areae widen somewhat from the 

 apex to the ambitus, and become slightly narrower from the ambitus 

 towards the mouth ; they are about 4 millims. in width at the 

 widest point, the lateral ambulacral spaces being 12 millims. 

 At the mouth the ambulacra expand into a very distinct floscclle, 

 and the interambulacral areae end in bourrelets crowded with 

 tubercles and bearing combs of long spatulato spines. The plates 

 of the apical disk are so compacted and fused together, that it is 

 difficult to trace their outline. Eight holes, nearly of equal size, 

 surround a central madreporic tubercle ; of these, five terminate the 

 ambulacra, and are the pits for the sense-organs, the other three are 

 ovarial. The posterior and the right anterior ovaries and ducts are 

 undeveloped. 



"The surface of the test is crowded with minute tubercles for the 

 articulation of the larger spines and many small granules. The 

 tubercles are imperforate, with a smooth mammillary boss ; they 

 are placed in circular scrobicular depressions, but they project some- 

 what above these and above the surface of the test. The larger 

 spines, articulated to the tubercles, are cylindrical, fenestrated, with 

 slight asperities on the longitudinal calcareous shafts. The small 

 spines which, attached to the minute granules, form a close under- 

 felting all over the test are fenestrated and slightly roughened, and 

 expand at the end into a rosette of pointed tubercles. The pedi- 

 cellariae articulated to some of the granules are three-valved ; they 

 are very small and of a somewhat peculiar form, though resembling 

 generally the smallest pedicellariae in Echinus. 



" The bases of the valves are wider, the valves themselves are 

 rounder and more arched and toothed round the edge. Round the 

 mouth there are groups of three and four very small pedicellariae, 

 differing in form somewhat, from the others, and with the bases of 

 the valves apparently fused together." 



I have not been able to trace this specimen, the account of which 

 as here given, is copied from Sir Wyville Thomson's description in 

 the ' Philosophical Transactions.' 



The species has been found at various depths between 100 and 

 229 fms. off the coasts of Florida. 



2. SCHIZASTER. 



Echinus (pars), Linn. Syst. Nat. x. (1758) p. 663. 



Spatangus (pars), Lamk. An. s. Vert. iii. (1816) p. 27. 



Ova, Gray, Ann. Phil. x. (1825) p. 431. 



Micraster (pars), Ag. Mem. Soc. Neuch. i. (1836) p. 184. 



Schizaster, id. t. c. p. 185 ; id. Sf Des. Ann. Sci. Nat. viii. (1847) p. 20 ; 



Al. Ag. Rev. Ech. (1872) pp. 157 & 363 ; Cams, Prod. Faun. 



Medit. (1884) p. 104; Duncan, J. Linn. Soc. xxiii. (1889) p. 234. 

 Periaster (pars), D'Orb. Pal. Franc, vi. (1854) p. 269. 



Test thin, generally longer than wide, highest posteriorly ; the 

 paired ambulacra sunken, and the anterior longer than the posterior, 

 the median in a deep groove ; two or three genital pores. 



m2 



