300 CATALOGUE OF THE BLASTOLDEA. 



of Astrocrinus is slightly truncated. But apart from the nature of the hydrospires, 

 Codaster is symmetrical, and has an anal opening (PL XIII. figs. 1, 4), which is 

 absent in the markedly asymmetrical Astrocrinus. Even with Elceacrinus, which 

 departs a little from the ordinary symmetry of the regular Blastoids, Astrocrinus has 

 nothing in common. In the former genus the modification is due to the intercala- 

 tion of an anal plate, all the ambulacra being alike (PL XVIII. fig. 19) ; but this is 

 very far from being the case in Astrocrinus. 



Species. We are acquainted with but two species of Astrocrinus : — 



Astrocrinites Benniei, Eth. Jn. Carboniferous Limestone ; South of Scotland. 



Astrocrinites tctragonus, T. & T. Austin. Carboniferous Limestone; Yorkshire. 

 Distribution. The genus is essentially a British one, and is confined to rocks of 

 Carboniferous age. 



Type. Astrocrinites tctragonus, T. & T. Austin. 



Astrocrinus tetragonus, T. & T. Austin. 

 (PL XX. figs. 1, 2.) 



Astracrinites tetragonus, Ann. & Mag. Nat. Hist. 1842, vol. x. p. 110. 



Astrocrinites tetragonus, T. & T. Austin, Ibid. 1813, vol. xi. p. 206. 



Astrocrinus tetragonus, Morris, Cat. Brit. Foss. 2nd edit. 1854, p. 72. 



Astrocrinites tetragonus, Etheridge, Jun., Quart. Journ. Geol. Soc. 1876, vol. xxxii. 1. 13. f. 26. 



Astrocrinus tetragonus, E. & C, Ann. & Mag. Nat. Hist. 1883, vol. xi. p. 237. 



Remarks. We are unable to frame a satisfactory diagnosis of this type owing to 

 the imperfect state of preservation of all the specimens which we have seen. There 

 are only two in the National Collection, and a few others in the Museums at York 

 and Liverpool. The Woodwardian Museum at Cambridge, the geological collection 

 at Owens College, Manchester, and that at Giggleswick Grammar School also con- 

 tain examples of the type which we have been permitted to examine ; and our thanks 

 are due to Prof. T. McK. Hughes, F.G.S., Prof. W. Boyd Dawkins, F.R.S., and to 

 the Rev. G. Style, M.A., for thus facilitating our work. The specific definition given 

 by the Messrs. Austin 1 contains the following passage: — "Near the centre of the 

 dorso-central plate is an oval eminence, apparently analogous to the madreporiforni 

 tubercle on the dorsal surface of the true Starfishes." The dorsocentral plate of 

 Austin is the azygos basal (x), but neither in this species nor in A. Benniei (PL XX. 

 figs. 8, 10, 13) have we found anything like the structure described by the Messrs. 

 Austin, and it is almost needless to observe that we should not expect to find a 

 madrcporic plate in any member of the Pelmatozoa. 



It is possible that the next species to be described, AMrocrinus Benniei, may be 



identical witli Austin's type, but as the characters of the former are well defined, and 



it is tolerably abundant in certain localities, and marks a well-known horizon, we 



prefer to regard the two forms as distinct from one another. So far, however, as 



1 Ann. & Mag. Nat. Hist. 1843, vol. xi. pp. 205, 20G. 



