B. W. PRIEST ON THE IIEXACTINELLID.E. 13 



bular, or ovate, and occasionally cup-shaped, varying according to 

 age, presenting a somewhat flattened summit in which there is 

 an aperture, and a conical base which is closed, but rendered irre- 

 gular by mammiform prolongations of the body, out of each of which 

 issues a hair-like lock of long anchoring spicules, sessile, or fixed by 

 the anchoring spicules ; colour grey ; external surface uniformly 

 even, except where interrupted by the mammiform prolongations ; 

 cribbellate immediately below the lattice-work layer, surmounted by 

 one form of spicule only, which issues, as before stated, in hair-like 

 locks from the summits of the prolongations ; internal surface of 

 the cavity uniformly smooth, interrupted by depressions so increas- 

 ing in size downwards as to occupy the whole of the lower part. 

 Structural spicules of the body or wall of three forms ; — first, a nail- 

 like or conically headed spicule, the shaft vertically placed in the 

 wall, and the arms spreading out horizontally over the external sur- 

 face, so as to support the lattice-like layer of minute sex-radiate 

 spicules imbedded in the dermal sarcode ; secondly, a long linear 

 spicule, often presenting in the middle two or four tubercles corres- 

 ponding to the ends of the crucial branches of the sex-radiate central 

 canal, terminating in spines, and more or less inflated extremities, 

 but otherwise smooth ; and thirdly, sex-radiates of different sizes, 

 with arms of ecpial length, spined and pointed, chiefly composing the 

 lattice-like structure and including the right rosette-like forms of 

 spicule of the sarcode. 



This species has also longer anchoring spicules than the other two, 

 with the four stout spines or hooks recurved and opposite, which 

 characterises the genus generally of Rossella. 



Another difference in the structure of the species consists in its 

 being without the veil of singular and beautiful form which is found 

 in the other species, extending about a centimetre from the surface 

 of the sponge, and formed by the interlacing of the four secondary 

 rays of the large five-rayed spicules, which send their long shafts 

 from that point vertically into the sponge body. 



Figs. 6, 7 and 8, PI. Ill, show forms of rosette occurring in 

 Rossella, and Figs. 5 and 7, the free end of the anchoring spicules 

 characterising the genus. 



The third family, or that comprising the characters of the two 

 forms combined, and of which only one species is, as yet, known, 

 viz., Evplectella cucumer, I shall pass over, as the sponge has been 

 well described bv Professor Owen in the " Linnean Transactions " for 



