NO. 2038. FOSSIL CRINOID OEIfUS HOMOCRINUS— KIRK. 481 



The existence of a potent primitive stock among the Crinoidea is 

 of large importance as determining evolution within that group. If 

 we extend our horizon the bearing of such a stock on the Pelmatozoa 

 as a whole presents features of even greater consequence. The inter- 

 relationships of the classes of the Pelmatozoa have always been a 

 matter of no little uncertainty — even to the extent of estabhshing 

 plausible connections between the classes. The solution of the 

 matter lies, I think, in the acceptance of a minute stock in which 

 fundamental modifications may well have taken place and from 

 which the various classes diverged more or less independently. 

 There is no reasonable objection to such an hypothesis and it has 

 much of the available evidence in its favor. 



It has generally been conceded that the Crinoidea have been 

 derived from the Cystidea, perhaps through the mediation of the 

 Blastoidea. Such may be the case — but not from the Cystidea or 

 Blastoidea as we know them. As we trace back any given crinoid 

 line, at least in that portion of the line antecedent to the acme of 

 the group, we find a uniform decrease in the size of the organisms. 

 Eventually we come to the small simple Inadunata. To evolve 

 these simple forms from the Cystidea as we know them is a contra- 

 vention of the fundamental laws of evolution. If we admit these 

 facts we must look elsewhere than among the known Cystidea for 

 the ancestors of the Crinoidea. The ancestors no doubt may have 

 had much the same structure as the Cystidea and evolved their 

 comparatively simple arrangement of plates by much the same 

 process that we may more or less readily trace in the elimination of 

 plates among the Cystidea. The whole evolution, however, was on 

 an infinitesimal scale. Did such types exist, as seems to be the 

 logical conclusion, one could style them perhaps "Cystidea", as that 

 term might broadly be defined. That there should be minute Cys- 

 tidea is no more improbable than that there should be minute Cri- 

 noidea — which we know exist. Such minute " Cystidea " might 

 well precede and give rise to the known Cystidea, as well as to the 

 other classes of the Pelmatozoa. 



Having shown Homocrinus to be a monocyclic Inadunate of quite 

 different affinities than has hitherto been supposed, it becomes neces- 

 sary to define a new genus for the reception of such forms as "H.^' 

 scoparius. For this genus I here propose the name Lasiocrinus, 

 taking scoparius as the type of the genus. For the time being but 

 two species wiQ be referred to the genus, scoparius and tenuis. The 

 systematic position of the other species called Homocrinus by Bather 

 (1893, p. 101) is doubtful. I have examined the types of ancilla 

 and cylindrica and at present feel disinclined to include them in the 

 same genus with scoparius. In a future more extended discussion 

 95278°— Proc.N.M.vol.46— 13 31 



