i 



234 Messrs. It. Etheridge, Jun., and P. H. Carpenter on 



but in the former these are replaced by a circular cavity, which 

 is filled in with calcspar, the remains of the upper stem-joints. 

 The interradial sutures extend downwards as far as this de- 

 pression, in which we may fairly expect that basal plates 

 would be found just as in some species of Granatocrinus. In 

 Mitra elliptica, as figured by Cumberland, the basals form by 

 far the largest portion of the flattened base, while in our 

 specimen this is chiefly formed by the inturned portions of 

 the radials. Under any circumstances Cumberland's figure 

 must be erroneous ; for no known Blastoid has more than the 

 normal number of three basals; and bearing this in mind, we 

 have little hesitation in referring our specimen to Cumber- 

 land's type. 



5. On the Genus Astrocrinus, T. & T. Austin (emend. 



Morris) . 



Astr ocr mites , T. & T. Austin, Ann. & Mag. Nat. Hist. 1842, vol. x. 



p. 112; ibid. 1843, vol. xi. p. 205. 

 Zygocrinus, Bronn, Index Pal. Nomenclator, 1848, p. 1381. 

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

 Astrocrinifes, Etheridge, jun., Quart. Journ. Geol. Soc. vol. xxxii. 



1876, p. 103. 



Ohs. Since the description by one of us, seven years ago, of 

 Astrocrinus Benntei, further examples of this remarkable type 

 have come to hand ; and the present state of our knowledge 

 of Blastoid morphology enables us to form a better idea of its 

 structure and systematic position than was possible in 1876. 



This aberrant member of the Blastoid group is distinguished 

 by the peculiar modification or apparently abortive condition 

 of one of the ambulacra. It was partly this feature which led 

 one of us, in describing A. Benniei, to regard its calyx as 



uadriradiate, although it is really quinqueradiate, as in all 



lastoids. 



Although Astrocrinus has been considered a Cystidean 

 by various paleontologists, we have little doubt that it is a 

 Blastoid and closely allied to the singular genus Eleuthero- 

 crinus of Shumard and Y andell *. As in that type, there are 

 four normal and linear ambulacra, together with an azygos 

 one of a somewhat different character, which was described 

 by Austin as the anus. In both genera the distal end of this 

 azygos ambulacrum is received in the scarcely perceptible fork 

 of a radial, which is shorter and broader than the other four, 



u Notice of a new fossil Genus belonging to the family Blastoidae, 

 from the Devonian Strata near Louisville, Kentucky," Proc. Acad. Nat. 

 Soc. Philad. vol. xiii. 1856, dd. 73-76. xA. ii. 







t *. 









y 



