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the Morphology of the Blastoidea. 237 



and as the fossils on which the name was based are not known, 

 no further notice need be taken of it. 



The description of Astrocrinus, given by the Messrs. 

 Austin, was considered bj Pictet * to indicate a complete 

 analogy with Codaster, but for the difference in the numbers 

 of the ambulacra. Pictet seems, however, to have entirely 

 forgotten the hydrospires of Godaster, though they had been 

 described and well figured by Romer. The only possible 

 resemblance between the two types is that the summit of 

 Astrocrinas is slightly truncated. But, apart from the nature 

 of the hydrospires, Codaster is symmetrical and has an anal 

 opening, which is absent in the markedly asymmetrical Astro- 

 crinus. Even with Eleaerinus y which departs a little from 

 the ordinary symmetry of the regular Blastoids, Astroerinus 

 has nothing in common. In the former genus the modifica- 

 tion is due to the intercalation of an anal plate, all the ambu- 

 lacra being alike ; and this is very far from being the case in 

 the Astrocrinida3. 



Two species of Astroerinus have been described — A. tetra- 

 yonas, T. & T. Austin, and A. Benniei, Etheridge, jun. ; but 

 it is quite an open question whether they are not identical. 

 The brief description given of the former is useless for pur- 

 poses of comparison ; but examples of it are very rare, and so 

 badly preserved that its true characters must still remain un- 

 certain. There is but one in the national collection, and a 

 very few others in the museums at Cambridge and York. On 

 the other hand, A. Benniei is tolerably abundant in certain 

 localities ; and its characters are fairly well defined. It marks 

 a well-known horizon in the Lower Limestone group of the 

 Carboniferous series in East and Central Scotland, where it 

 was discovered some years ago by Mr. James Bennie.^ The 

 doubtful species, A. tetragonus, occurs in the Carboniferous 

 Limestone of Yorkshire, and is said to have been first obtained 

 at Settle. 



6. On the Genus Stephanocrinus, Conrad, 1842. 



Stephanocrinus, Conrad, Journ. Acad. Nat. Sci. Philad. 1842, vol. viii- 

 p. 278 ; Romer, Wiegmann's Archiv, 1850, Jakrg. xvi. pp. 365-375, 

 Taf. r. ; Hall, Pateontology of New York, 1851, vol. ii. p. 212. 



Obs. In Homer's admirable account of Stephanocrinus 

 angulatus the radials are rightly described as fork-shaped, 

 with the two contiguous limbs of adjacent forks produced up- 

 wards into strong interradial processes ; and the manner m 



* Traite de Pnleontologie, vol. iv. p. 295. 



