256 CATALOGUE OF THE BLASTOIDEA. 



anal spiracle (PL VI. fig. 5), though we should not like to speak positively upon 

 this point. 



The spiracles of Heteroblastus are thus in pairs like those of Schizoblastus. But 

 instead of leading downwards into the radial sinus beneath the ambulacra, as in most 

 Blastoids, the hydrospire-canals of each interradius first approach one another in 

 grooves on the inner faces of the deltoids (PL VI. fig. 4) ; and it is in consequence 

 of their relation to these plates that we have associated the genus with Granatocrinus. 

 Its ambulacra are rather more petaloid than in that type, and in our British species 

 they are depressed some little way below the edges of the wide radial sinuses which 

 slope down to meet them (PL VI. figs. 1, 2). So far as we can make out, all these 

 characters are repeated in a Blastoid from the St. Louis Limestone of Illinois, which 

 was described by Meek and Worthen 1 in 1861 as Pentremites cornutus, and was 

 afterwards referred to Granatocrinus 2 . We quote their description — " Radial pieces 

 .... very thick and rising into prominent carina? on each side of the pseudo-ambu- 

 lacral fields. Interradial pieces of moderate size, and each projecting out in the form 

 of a very prominent, compressed horn-like process. Pseudo-ambulacral areas very 

 narrow or lance-linear, and deeply implanted between the very prominent carinated 

 forks of the radial plates." The summit of this species is unknown, but the side view 

 of it, which is given by Meek and Worthen, is remarkably like our Heteroblastus 

 Cumherlandi (PL VI. fig. 1), especially in the appearance of the ambulacra and of 

 the radial sinuses. It has smaller deltoids, however, these being confined to the 

 large processes round the peristome, instead of forming the greater portion of the 

 calyx as in our species. 



We are indebted for the material on which we have established Heteroblastus to 

 our friend Mr. James Bennie, of the Geological Survey of Scotland, who discovered 

 the specimens in 1884, and has thereby added a new genus to the British Blastoid fauna. 



Distribution. The genus is limited in England to the Yoredale shales of North- 

 umberland, but there seems to be a second species in the Subcarboniferous system of 

 America. 



Species. We place the two following forms under this genus : — 



Heteroblastus Cumbcrlandi, sp. nov. Yoredale Shales, Carboniferous Limestone : 



Northumberland. 

 % Pentremites cornutus, M. & W. St. Louis Limestone, Subcarboniferous: 

 Illinois. 



Type. Heteroblastus Cumbcrlandi, sp. nov. 



1 Proc. Acad. Nat. Sei. Thilad. 1861, p. 141. 



- Report Geol. Survey Illinois, 1SCG, vol. iii. p. 276, pi. 20. fig. 1. 



