GEOLOGICAL AM) GEOGRAPHICAL DISTRIBUTION. 133 



(5) The appearance of other genera which are peculiar to each area respectively, 

 viz. : — Cryptoachisma and Phcenoschisma in Europe ; Codaster, Eloeacrinu3, Eleuthero- 

 crinus, and perhaps also Granatocrinus and Schizoblastus in America. Three" of these, 

 Cryptoschisma, Elasacrinus, and Eleutherocrinus, are exclusively Devonian genera. 

 Phcenoschisma passes up into the Carboniferous of Belgium, England, Scotland, and 

 America ; while two at least of the other three types occur abundantly in the 

 Carboniferous of both Britain and America. 



(6) The Devonian Blastoids of America are slightly more numerous, both in genera 

 and in species, than those of the European area, though not greatly so. 



The Carboniferous rocks of the British Islands are particularly rich in Blastoidea, 

 no less than ten genera being therein represented. Only one of these, Phcenoschisma, 

 is also found in the European Devonian, whilst from American rocks of that age 

 there pass up Codaster, and also Schizoblastus and Granatocrinus (fide Shumard). 

 In addition to these, there are the peculiarly British genera Acentrotremites, Pente- 

 plnjUum, and Astrocrinus. Pha noschisma, Orophocrinus, and Mesoblastm are common 

 to America. Britain, and Belgium. Hetcroblastus is perhaps found in America, while 

 Pentremites, strange to say, is not a British genus at all, its place, as regards the 

 relative abundance of species, being apparently taken by Granatocrinus and Meso- 

 blastus together. 



The whole of the genera mentioned are confined to the Carboniferous Lime- 

 stone, and we know of no trace of Blastoidea from the Lower Carboniferous (or 

 Calciferous Sandstone Series), much less from any of the marine bands of. the Coal- 

 Measures. 



Pentremitidea does not occur in the Carboniferous rocks, and it appears to have 

 died out at the close of the Devonian period ; though Phamoschisma is represented by 

 two of the six described species Two species of Schizoblastus have been met with 

 in the Irish Limestones, but it is not known in the English beds, which contain. 

 however, the allied genus Acentrotremites. Granatocrinus, on the other hand, has 

 increased in the number of species, and may be looked upon as the typical British 

 genus, being individually much more abundant than Mesoblastus, of which there are 

 also five British species. Oroi>hocrinus has three representatives in this country, 

 and is of interest from its extended geographical range. Codaster, although not rich 

 in species, is a genus of importance, from the large number of individuals which 

 occur in certain localities. The curious little irregular genus Astrocrinus, the 

 surviving representative of Eleutherocrinus from the Devonian of America, has only- 

 been met with, so far as we are aware, in the Carboniferous Limestone Scries of 

 England and Scotland; while PentcpJty/tum is peculiar to the same horizon in 

 Ireland. We have not met with any evidence of either Troostocrinus, Triceelocrinus, 

 or Jfctabtastus in the British Carboniferous rocks. 



Little remains to be said of the Blastoidea met with in the Continental Carboniferous 



