GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION. 129 



CHAPTER VII. 



THE GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION OF 

 THE BLASTOIDEA. 



We have no certain evidence of the existence of true Blastoidea anterior to the 

 Upper Silurian period. For we much doubt, as we have explained in the previous 

 Chapter, whether the problematical Blastoidocrinus from the Lower Silurian of 

 Canada and Russia can properly be referred to this group. 



It is curious that all the known Blastoids of the Upper Silurian period are confined 

 to American strata. None have been found in the Wenlock Limestone of Britain, 

 though representatives of two, or probably of three, genera occur in the Niagara Group, 

 which is the corresponding formation in America. One of these is Codaster, if, as 

 we believe, the Codaster pulchellus of Miller and Dyer l from Waldron, Indiana, 

 is rightly named. An internal cast from this horizon, which has been described by 

 Hall and Whitfield-, from Ohio, together with an imperfect specimen figured by 

 Hall 3 from Indiana, appear to us to be referable to the Troostoblastidoe, though we 

 cannot venture to give them generic names. In the Niagara Group of Tennessee, 

 however, well-preserved examples of Troostocrinus Reinwardti are not uncommon. 



We are not acquainted with the presence of Blastoids in the Upper Silurian rocks 

 of any other part of the world than North America. This is the more striking when 

 we recollect the great development of Crinoid life which took place during the 

 Wenlock Period in Europe, especially as represented by the Wenlock Series of 

 England and of the island of Gotland. 



The Devonian rocks of the British Islands have yielded but the scantiest evidence 

 of Blastoid life, and we are not in a position to affirm with certainty the generic 

 relations of the specimens hitherto found. The late Prof. J. Phillips 4 described one 

 species from the Pilton Group (Upper Devonian) of North Devon, which he referred 

 to Pentremites ovalis, Goldfuss. We have not been able to trace this specimen, and 



1 Contributions to Palaeontology. Journ. Cincinnati Soc. Nat. Hist. 187S, vol. i. no. 1. p. 35, pi. 2. fig. 13. 

 See also Hall, in Collett's 11th Ann. Report Dcpt. Geol. & Nat. Hist. Indiana for 1881 [1882], p. 280, 

 pi. 15. figs. S-10. 



2 Pentremites subcylindrica (Ohio Geol. Report, 1875, vol. ii. part 2. p. 129, pi. vi. fig. 13). 

 » Codaster pentidobus (Collett's 11th Report, he. cit. p. 280, pi. 15. fig. 16). 



* Pal. Foss. Cornw., Devon, and "W. Somerset, 1841, p. 29, t. 14. f. 40. 



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