232 Messrs. B. Etheridge, Jun., and P. H. Carpenter on 



though they are much smaller in S. melo, S. neglectus, and 

 S. pisum. The first of these three species has only eight 

 spiracles, the remaining two being confluent with the anus. 

 The independence of the anus in the two latter species is not 

 certain; but in any case, as in S. Sayi, the spiracles are 

 formed exclusively by the edges of the oral plates, while in 

 Acentrotremites they are partially bounded by the radials. 

 This type also resembles Troostocrinus in the presence of a 



\ 



4. A new Genus of British Carboniferous Blastoids. 



Genus Acentrotremites, gen. nov. 



Gen. char. Calyx large, elliptical, and flattened at the 

 base, generally resembling that of Granatocrinus in the form 

 and proportions of its component plates. Spiracles ten in 

 number, and remote from the apex, being placed at the points 

 where the oro-radial sutures meet the somewhat narrow am- 

 bulacra. Anus distinct, and situated at the apex of the 

 oro-anal plate* Hydrospires, appendages, and column un- 

 known. 



Obs. We have established this genus for a very remark- 

 able type from the Carboniferous Limestone, which resembles 

 Granatocrinus in general appearance, and especially those 

 species like G. Norwoodi and G. angulatus, which have rela- 

 tively large radials and small orals. But the summit-cha- 

 racters of Acentrotremites are entirely different from those of 

 Granatocrinus ; for it has a distinct anal opening, which pierces 

 one of the oral plates, and ten spiracles as well ; while the 

 anus of Granatocrinus is confluent with one of the spiracles, 

 and these openings, except in G. Bqfei, are single and not \ 



paired. They are also close to the peristome, and actually 

 pierce the substance of the oral plates. In Acentrotremites, 

 on the other hand, the spiracles are some little way from the I 



peristome, so as to be visible in a side view of the calyx. 

 About one fifth of the whole length of the ambulacra lies 

 between them and the radial centre ; and they merely notch 

 the lower lateral angles of the oral plates where these join the 

 radials. The result of this must be that the proximal ends of 

 the hydrospiral tubes are situated at a point much lower in 

 the calyx than is generally the case in the Blastoidea. 



Acentrotremites perhaps approaches most closely to Schizo- 

 blastus, and especially to S. Sayi, which also has ten spiracles 

 at some little distance from the peristome and a distinct anal 

 aperture. The orals of this species, however, are enormous 



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