[2 INTKOIM < Th'N. 



the more important contrast between the Crinoids and the rest of the 

 Echinoderms which has been mentioned by older naturalists, like W. B. 

 Carpenter, Huxley, Metschnikoff, and other writers on the embryology of 

 Echinoderms. 



Say bad most definite views of the position of Blastoids as a family of 

 Crinoids. yet lie still associated the Cyst ids with the Brachiate Crinoids. 



From Vim Buch's .Monograph on the Cystids it is evident that, while 

 lif recognizes their affinities to the Crinoids, yet he also insists on their 

 structural differences, and comes to the conclusion that they stand alone 

 at the beginning of the series formed by the succession of the Crinoids 

 to the Cystideans. 



Roemer, however, who made the first exhaustive study of the Blastoidea, 

 placed them as a family in the order of Crinoidea, as the title of his 

 memoir sufficiently shows, '• Monographic der fossilen Crinoiclen, Familie 

 der Blastoiden." Whether the Blastoids and Cystids are sufficiently dis- 

 tinct to rank as separate classes is more than doubtful, considering, as 

 Carpenter says, the large number of apparently intermediate forms which 

 have been discovered since Roemer wrote. Carpenter himself (Chall. Rep., 

 p. 191) mentions the difficulty of referring forms like Hybocystites and 

 Cystoblastes to one group rather than the other. 



The existence of arms, although but slightly developed, and of an artic- 

 ulated stem, and the discovery of several so called transition types between 

 the Brachiate Crinoids and the Cystids would seem sufficiently to indicate 

 their affinity with the Eucrinoids, in spite of the incomplete radial struc- 

 ture of the plates of the body and the presence of the so called hydrospires. 

 Similarly, the presence in the Blastoids of pinnules, which are after all only 

 modified arms, would also indicate a closer structural affinity with the 

 Brachiate Crinoids than Carpenter is willing to admit when contrasting 

 the Blastoids and Cystids, as a subdivision of Echinoderms, with the Bra- 

 chiate Crinoids.* 



* See also Etheridge and Carpenter, Catalogue of the Blastoidea of the British Museum, 1886. 



