188 CATALOGUE OF THE BLASTOIDEA. 



concave in the middle line, their apices forming a portion of the truncated summit ; 

 anal deltoid only concave at its extreme (radial) end ; radio-deltoid sutures sharply 

 V-shaped. Ambulacra curved, and projecting above the edges of the sinuses ; lancet- 

 plates prominent, the steep sides projecting in a similar manner when the side-plates 

 are removed ; side-plates thirty-five to forty, inclined at a high angle. Hydrospires 

 unknown. Anterior spiracles oval, in four pairs, divided by strong deltoid ridges ; 

 anal spiracle with an outer raised lip-like margin. Mouth indistiuctly preserved, but 

 apparently small. Ornament of radial plates not preserved, but probably lineate 

 granular ; deltoid plates with strong V-shaped stria;. 



Remarks. We were formerly inclined to regard this form merely as a variety of 

 M. oblongus, with an abnormally protuberant base. But on investigating the subject 

 more minutely, it became apparent to us that this character, in conjunction with the 

 more expanded outline of the calyx, and the more inflated and, to some extent, 

 narrower ambulacra, demanded more than varietal separation. 



Mr. G. B. Sowerby distinctly described the base of M. elongatus (as Pcntatrematites 

 oblonga) as being concave ; he says, " The pelvis is small and concave." In the 

 present form, though certainly not large, it is very distinctly protuberant (PL VI. 

 tig. 12). The interradial areas of M. Soiverbii are much broader than in M. elongatus 

 (PI. VIII. fig. 1), and the ambulacra, which in the latter type are somewhat depressed 

 below the edges of the sinuses, project a good deal beyond them in the present species. 

 It is also probable, judging from the structure of M. cremdatus, that the protuberant 

 base will become a feature of some importance and specific value in this group. 



The mouth seems to be unusually large in our best specimen of M. Soiverbii 

 (PI. VI. fig. 13), but it has perhaps been artificially enlarged. The four anterior 

 spiracles are pretty distinctly double, as the narrow deltoid ridge almost comes right 

 down to the peristome. 



A curious structure, which we cannot make out, is seen beneath the broken surface 

 of the deltoid in the specimen shown on PL VIII. fig. G. We thought at first that 

 it represented the casts of the two converging hydrospire-canals, as in Granatocrinas 

 Norwood! (PL VII. figs. 7-9). But this is certainly not the case, for these canals in 

 other specimens can be seen to reach the spiracles beneath the hydrospire-plates, 

 which are well shown in this same individual. 



We have much pleasure in naming this species after the late Mr. George Brettingham 

 Sowerby, who was the earliest writer on British Blastoids, with the exception of Mr. G. 

 Cumberland, of Bristol. 



Locality and Horizon. Bolland District, Lancashire : Carboniferous Limestone. 



MESOBLASTUS PiOFKI, sp. 110V. 



(PL IV. figs, o, 4.) 

 Acentrotremites, sp., E. & C, Ann. & Mag. Nat. Hist. 18*5, vol. xi. p. 2:33. 

 Sp. Char. Calyx roundly acorn-shaped, much arched along the ambulacra, and 



