120 CATALOGUE OF THE BLASTOIDEA. 



four plates each below the radials, and some of them pierced by the hydrospire-slits. 

 Other slits occur at the sides of the radials, but transversely to the ambulacra, while 

 there are only four deltoids, which are in the same line with the radials and not above 

 them. We cannot see any very striking Blastoid affinities here. The same may be 

 said of Asteroblastus. This type has four basals and five deltoids, the two series being 

 separated from one another by a group of small plates. The ambulacra and pinnules 

 are at least as much like those of Pseudocrinites and other Cystids as those of any 

 Blastoid. Asteroblastus has no lancet-plate nor intenadial hydrospires ; and we do 

 not think that the " ambulacral pores " mentioned by AVachsmuth and Springer 1 are 

 what that name implies, since we take them to be the sockets for the attachment of 

 the pinnules, as was described by Schmidt 2 , who further said " auf den Radien selbst 

 keinerlei Poren." Lastly, as the small calycular plates above mentioned bear the 

 well-known " double pores," we fail to see what characters, besides the very 

 generalized one of five pinnule-bearing ambulacra, do link Asteroblastus with the 

 Blastoidea. Hybocystites is another type which in some respects is very like a 

 Blastoid, but the resemblance is more a superficial than a fundamental one, and we 

 are inclined to regard it as less like a Blastoid than was thought by one of us in 

 1SS2 3 . The pentamerous base on which two or more of the ambulacra terminate, the 

 segmented extensions of three rays, and the azygos plates, all seem to us to suggest 

 that the resemblance to a Blastoid is in a great degree superficial, and due rather 

 to the appearance of the ambulacra than to any definite morphological characters. 



There are various Lower Silurian forms from the Trenton group which are allied 

 to Hybocystites and Ilemicystites, and have been thought to represent a primitive 

 Blastoid type. By the kindness of Professor "Wetherby we have been permitted to 

 examine some of these ; but we cannot make out that they have any claim to 

 admission into the very well-defined group Blastoidea. At the same time they are 

 very different from the ordinary Cystids. This name is applied to a number of very 

 different types ; and we quite agree with Wachsmuth and Springer that a further 

 subdivision of von Buch's original group is now necessary. 



The only described form which appears to us to offer any real link between the 

 Blastoids and the Crinoids or Cystids is the problematical lilastoidocrinus. So far as 

 we are able to understand its characters from the descriptions of Billings 4 and 

 Schmidt 5 , it must be somewhat similar in form to Orqphocrinus jpentangularis, but 



' ' Revision of the Falacocrinoidea,' Tart III. 1885, p. 7<J. 



2 "Ueber einige neue uud wenig bekannte Baltisch-Silurische rctrefacten." Mem. Acad. Imp. Sci. St. 

 Petersbourg, 1S74, vii.° ser. torn. xxi. Mem. 11, p. 29. 



8 " On the Relations of Hyboerinm, Baerocrinus, and Hybocystites," Quart. Journ. Geol. Soc. 1882, vol. 

 xxxviii. pp. 311, 312. 



"On the C'rinoidesD of the Lower Silurian Rocks of Canada. - ' Figures and Descriptions of Canadian 

 Organic Remains, Decades Geol. Survey Canada, no. iv. ISot), pp. 18-21. 



6 Loe. cit. p. 27. 



