192 THE VOYAGE OF H.M.S. CHALLENGER. 



which they had been raised by Forbes, they had been, and were subsequently, still further 

 degraded. For d'Orbigny^ took an entii'ely different view of the characters of the 

 various types of the Pelmatozoa from those held by some of his predecessors ; and he not 

 only threw the Cystids and Blastoids back among the Crinoids, but he considered these 

 two groups merely as families. He divided the order Crinoidea into twelve families, 

 among which are the Comatulidse, Pentremitidae, Cystidse, and lastly the Pentacrinidae ; 

 and Pictet ^ subsequently reduced this number to nine, but without making any change 

 in the four above mentioned. 



Dujardin and Hupe '' also adopted this singular arrangement, according to which the 

 differences between a Pentacrinus and a Pentremites, Pchinosjyhcentes or Actinocrmus, 

 are of no greater systematic value than those between Pentacrinus and Comatida. In 

 this country, however, thanks mainly to the teaching of Prof. Huxley,* Crinoids, Cystids, 

 and Blastoids have always been regarded as independent but equivalent divisions, 

 formerly orders, but now' classes of the Echinodermata. To these Huxley * has since 

 added another, as to the necessity for which there has been a considerable difference of 

 opinion, viz., the Edriasterida. 



This group, which includes the curious sessile forms Agelacrinus, Edrioaster, and 

 their allies, has been generally placed among the Cystids ; but it has been re-established 

 quite lately under the name of Agelacrinoidea by S. A. Miller, in ignorance of Prof. 

 Huxley's classification of fifteen years ago. 



I am inclined to think myself that if these forms be anything more than the 

 isolated disks of Palseocrinoids, as was thought possible by Sir Wy\^ille Thomson [ante, 

 p. 85), theii- proper place is among the Cystids. 



Two other new orders (i.e., classes) of the class [i.e., subkingdom) Echinodermata have 

 recently been proposed by S. A. Miller.* These are the Lichenocrinoidea and the 

 ]\Iyelodactyloidea. But I cannot regard them as of equal value with the Crinoids, Cystids, 

 and Blastoids. Our knowledge of the structm'e of Lichenocrinus is of the most limited 

 character ; and it is therefore totally insufficient for the basis of a class definition. The 

 same may be said of Cyclocystoides, which together with the so-called Myelodactylus is 

 placed by Miller in a new order that he proposes to call Myelodactyloidea. Wliatever 

 be the nature of Cyclocystoides, there can, I think, l)e little doubt that Salter, 

 Charlesworth, and more recently Nicholson and Etheridge ^ were right in regarding the 



1 Oours elimeutaire de Paleontologie et de Geologie stratigraphique, Paris, 1852, t. ii. fasc. i. p. 134. 

 - Traite de Paleontologie, t. iv. p. 282. 



^ Histoire Naturelle des Zoophytes, Echinodermes, Paris, 1862, pp. 55-58. 

 ■* Lectures on General Natural History, Medical Times and Gazette, November 1856, p. 463. 

 '" An Introduction to the Classification of Animals, London, 1869, p. 130. 



^ Description of three New Orders and four New Families, in the class Echinodermata, and eight New Species 

 from the Silurian and Devonian Formations, Journ. Cincinn. Soc. Nat. Hist., vol. v. jjp. 221-223. 



^ A Monograph of the Silurian Fossils of the Girvan District in Ayrshire, Edinburgh, 1880, pp. 330-334. 



