1030 Dit. j. vt. anEaouT on tee CLA.saii?ioAiiON [Dec. 15 



those of Asterids and of the Echinid Palceocliscus. As the two 

 elements which have fused to form the vertebral ossicles of later 

 Ophiurids are unattached in the members of this order, I propose 

 for it the name Lysophiuras '. 



No one has worlced at the Palasozoic Ophiurids without being 

 impressed by the unsatisfactory natui-e of many of the genera. 

 In my earliest pateontological paper (1889) I pointed out that 

 Frotaster would have to be split up into more than two genera 

 [6. p. 27J. Sturtz, both in 1890 [16. p. 245] and 1893 [17. p. 19], 

 also insisted that Frotaster includes a miscellaneous group of 

 species, and that the Protasters of Forbes, Billings, Hall, and 

 myself are distinct. I shrank from the task of dismembering this 

 genus in 1889, as I hoped for better specimens of the type species. 

 None such, however, have been forthcoming. As I am now 

 bound to attempt to indicate the relations of the fossil and recent 

 forms in an account of the Ophiuroidea for Prof. Lankester's 

 ' Oxfoi'd Natural History,' I delay no longer. In order to 

 simplify my task in that place, I offer the following synopsis of 

 the classification of the Palaeozoic Ophiurids, with diagnoses of 

 some of the genera. 



Order I. LYSOPHIUEiE. 



Diagnosis. — Ophiuroidea of which the ambulacra! ossicles are 

 alternate and are not united into vertebral ossicles. There are no 

 ventral arm-plates, and the underside of the arm is occupied by an 

 ambulacral furrow. 



Eemar/cs. — This order includes a group of Palteozoio Ophiurids 

 in which the arm-structure is on the same plan as in the Asterids ; 

 for there are no ventral arm-plates, there is an ambulacral groove, 

 and the ambulacral plates are in double series. Tbe members of 

 the order differ from the Asterids by having the arms sharply 

 marked ofE from the disc ; while the alimentary canal was, in all 

 probability, entirely limited to the disc. 



So far as is known at present, the order was limited to the 

 Palajozoic period ; but it is necessary to consider whether a few 

 recent forms ought not to enter it. In Ophiohelus and Ophiotholia 

 the ambulacral plates occur as pairs of rod-like plates, instead of 

 as vertebral ossicles. They therefore, in this respect, resemble 

 Lysophiurids. On application to the- Zoological Department of 

 the British Museum, I find that both genera are represented only 

 by the small single specimens dredged by the ' Challenger.' It is 

 too groat a responsibility to subject these fragile type specimens 

 to the risk of re-examination, especially as the nature of the 

 articular surfaces could not be determined without dissection. 

 Both specimens are so small, that, as Prof. Bell suggests, it is quite 

 possible they are not mature. 



The members of tbe two genera, however, differ from the 

 Pateozoic Lysophiuras in three respects : they have the ambulacral 



^ From Xvffis, dissolution, unattuchmeut. 



