1548 THE VOYAGE OF H.M.S. CHALLENGER. 



which I describe here as Cannopilus (PL 114, figs. 7-13). All these peculiar forms may 

 be derived from the simple annular pieces of skeleton, which are aggregated in great 

 numbers in the calymma of Mesocena. The pieces of the skeleton of these Dictyochida 

 never assume the form of slender, cylindrical, tangential tubules which is characteristic 

 of the Cannobelida, 



A third subfamily of Cannorrhaphida, the Catinulida, is represented by the remark- 

 able new genus Catinulus (PL 117, fig. 8). The single pieces of the skeleton, scattered 

 in hundreds or thousands throughout the calymma, are here not composed of hollow 

 rods, as in the two former subfamilies, but are solid hemispherical caps, or small, more 

 flatly vaulted dishes, with a peculiar radial striation. All the complete specimens of 

 Catinulus which I could examine possessed four equal central capsules, united in one 

 spherical calymma. 



The common character which unites the three rather different subfamilies, the 

 Cannobelida, Dictyochida and Catinulida, into a single family, and which separates this 

 family, the Cannorrhaphida, from the other PH^EODAEIA, is to be found in the composition 

 of the rudimentary skeleton from numerous single pieces, which are loosely scattered 

 either on the surface of the calymma, or throughout its jelly-mass, and which are never 

 arranged radially, and never touch the central capsule, as is always the case in the closely 

 allied Aulacanthida. 



The slender spicula of the Cannobelida are cylindrical or spindle-shaped, tubular, 

 scattered in variable numbers, but always in a tangential direction on the surface of the 

 calymma. Usually they are 0'2 to 0'5 long, and 0'005 to 0'03 broad ; either straight or 

 slightly curved ; smooth and simple in Cannobelos, spiny or branched in Cannorrhaphis 

 (PL 101, figs. 3-5). Their wall is thin and fragile, their diameter sometimes equal 

 throughout their whole length, at other times tapering towards both ends. Their cavity 

 is filled by jelly, and seems to be open at both ends, since the purified and dried spicula 

 constantly become filled by air. 



The peculiar pieces of silica which compose the skeleton of the Catinulida are not 

 hollow, like the rods of the other Cannorrhaphida, but concave hemispherical cups or more 

 flatly vaulted little dishes, the thin flinty wall of which is slightly thickened at the 

 circular margin, and radially striped above it. In all three species of Catinulus observed 

 they were scattered throughout the calymma in hundreds or thousands (PL 117, fig. 8). 

 Their relation to the Dictyochida is doubtful. Perhaps the small cups of Catinulus may 

 be derived from the simple rings of Mesocena, by development of an operculum on one 

 side of the ring. 



The skeleton of the Dictyochida is much more developed and possesses a higher 

 morphological interest ; the numerous different forms, however, which its pieces here 

 assume, may be all derived from the simple circular ring of Mesocena. This ring is 

 formed by a thin, hollow, cylindrical, or prismatic rod, sometimes circular or elliptical, at 



