330 



lamily 9.— ECHINOBRISSIDtE, Wright, 1856. 



Famille des Cassidulides, growpe des Nucleolides, Agassiz and Besor, 1846. 

 Famille des Nucleolidees (in pars) Albin Gras, 1848. 

 Famille des EcHiNOBKissiDiES (in pars) jyOrhigny, 1855. 



The family EcHiNOBnissiDiE, as I have defined it, comprehends only those urchins 

 which have petaloidal or sub-petaloidal ambulacra ; the vent lodged in a dorsal sulcus, 

 or opening at the posterior border ; the mouth edentalous ; and the peristome pentagonal 

 and sub-central. 



The test, in all the smaller species, is thin, has a sub-quadrate, oblong, sub-pen- 

 tagonal, circular, or clypeiform shape ; is uniformly covered with small imperforate 

 tubercles, raised on uncrenulated bosses, and surrounded by deep sunken areolas (PI. XXIV, 

 fig. 1 h) ; the spines are small, short, and slender (PI. XLI, fig. 1) ; the tubercles at the 

 base are always larger, and more fully developed, than those on the upper surface. 



The ambulacral areas are narrow and lanceolate ; they are enclosed by poriferous 

 zones of unequal width, the pores being placed more or less wide apart in different 

 regions of the zones ; the holes of the inner row are circular, those of the outer are oblong 

 or slit-like, and they often communicate with the inner series by transverse sulci. In 

 consequence of this structure, the ambulacra present elegant petaloidal forms, more or less 

 developed in different species, but always lanceolate above, expanded in the middle, and 

 contracted and open below. The poriferous zones at the border and base are narrow, 

 and the pores are small, equal, and placed wide apart (PI. XXIV, fig. 1 i). 



The apical disc is in general small, and composed of at least ten elements ; of the five 

 genital plates, four are perforated, and one is imperforate ; the right antero-lateral plate is 

 always the largest and carries the madreporiform tubercle, which is often very large, and 

 nearly conceals the other elements of the disc ; the five ocular plates are small, with 

 marginal orbits (PI. XXIV, fig. 1 (j), placed opposite the apices of the ambulacra. 



The vent is large, and in general opens into a valley situated in the upper surface of 

 the inter-ambulacrum, or at the middle or margin of the posterior border ; in the only 

 living species at present known, Nudeolites recens, Edwards, from New Holland, figured in 

 the illustrated edition of the ' Regne Animal/ this aperture is found to be closed by a series 

 of small plates, in the same manner as the anal aperture is filled up in the Echinid^ and 

 Spatangid^. I have copied this figure in PL XLI, fig. 1 a, and a specimen of the urchin, 

 without spines or anal plates, is now in the collection of living Echinoderms in the British 

 Museum. 



The mouth-opening is small, sub-central, and edentulous ; the peristome in general is 

 pentagonal, and in the genus Clypeus is surrounded by five oral lobes (PI. XXVIII, fig. 

 1^). 



