. 



238 Messrs. R. Etheridge, Jun., and P. H. Carpenter on 



which this type might be derived from such a form as Troosto- 

 crinus lineatus or T. Reinwardti is clearly pointed out. 

 HalPs description of this singular fossil, written at about the 

 same time as Homer's, was, however, far more complicated. 

 He regarded the radials as comparatively small, and the upward 

 processes as formed by hypothetical u scapular plates ;" though 

 most of his figures show the interradial suture along the middle 

 of each process. He admitted indeed that the . " scapular 

 plates" might be double; but he seems never to have re- 

 garded them as actually part of the radials. The supposed 

 sutures between the costal and scapular plates are probably 

 only the surface markings which are found in so many Blas- 

 toids (Granatocrinus elongatus^ Codaster pyramidatus, Oropho- 

 crinas Orbignyanus, Phcenoschisma Archiacij &c.) extending 

 downwards from the radial lip to the upper angles of the sub- 

 jacent basals. After becoming acquainted with Homer's 

 memoir, Hall seems to have tacitly adopted his views respect- 

 ing the structure of the calyx ; for a small diagram of S. 



ifi 



*, differs in 



toto from those which appeared in the i Palaeontology of New 

 York,' and shows the fork-shaped radials more in their proper 

 aspect, 



S. angulatus is, in fact, a Blastoid with an unusually deep 

 radial sinus, owing to the excessive development of the radial 

 limbs. The sides of the sinus are much steeper than in 

 Phcenoschisma, and are not marked by hydrospire-slits ; but 

 the ambulacra are quite short and nearly horizontal, as they 

 are in Codaster acutus and Phcenoschisma Archiaci, instead 

 of bending downwards as they do in other species of 

 both these genera. Their distal ends are received in a 

 rather strongly marked radial lip, which was thus described 

 by Hall : — " The upper margins of the costal plates are 

 excavated in the middle, and on their inner margin sup- 

 port a small semicircular plate." Homer described this 

 structure as a reniform scar for the attachment of an appen- 

 dage — an explanation which seems unlikely, now that Hall has 

 discovered ambulacra! appendages in Stephanocrinus like 

 those of other Blastoids. We think ourselves that the part 

 in question is nothing more than an infolded radial lip, which 

 is rather more strongly developed than usual, and is much 

 more distinct in some specimens than in others. Something 



Mus 



am 



figs. 15, 20(1879). The documentary edition of this report, which coc 

 the plates but no text, appeared in 1876. Both text and plates have been 

 reproduced in the 11th annual report of the i State Geologist of Indiana,' 

 1882. 





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