378 Mr. F. A. Bather on British Fossil Orinoids. 



accompanying Table (I.) of Geological Distribution. The 

 American rock series has been taken as the most convenient ; 

 for the horizons of the various fossils are more distinct and have 

 been more carefully noted by American geologists, and Crinoids 

 appear to be found in America at more horizons than in 

 Europe. The horizons or localities of extra-American genera 

 are noted in brackets: W. L. = Wenlock Limestone and 

 M. L. = Mountain Limestone. To those who have read care- 

 fully the earlier part of this paper, a mere inspection of this 

 table will suggest the various lines of descent. So far as 

 positive evidence goes there is nothing here to conflict with 

 the history of evolution in various structures as sketched out 

 in preceding sections. There are of course gaps in the chain 

 of evidence ; but these were to be expected. Their slight 

 importance is brought out more clearly by the plan here 

 adopted of printing the name of a genus only opposite those 

 strata in which it has actually been found. Calceocrinus for 

 instance, which is known in the Niagara and Wenlock Lime- 

 stones and which persists with slight modifications to the 

 Keokuk, must have been living in the Waverley, Chemung, 

 and Helderberg eras. Till it has been discovered we need 

 not hope to find forms intermediate between, say, Botryocrinus 

 and Vasocrinus. Moreover the sudden appearance in the 

 Trenton Limestone of no less than 9 genera, all very distinct 

 from the 3 rare genera found in earlier rocks, is an obvious 

 indication of a series of Cambrian ancestors as yet known 

 only by a few undecipherable fragments : it is as unnecessary, 

 as it would be absurd, to derive all these from Eybocrinus and 

 Soplocrinus. 



Among the forms known from the Trenton and earlier rocks 

 are both Monocyclic and Dicyclic genera. I have already 

 given reasons to show that Monocyclica may have been derived 

 from Dicyclica (p. 318 ante) ; but the table shows that certain 

 Monocyclic forms are actually the earliest known, viz. Hybo- 

 crinus, Hoplocrinus, and Baerocrinus. Now these forms 

 differ so markedly, both in the arm-structure and in the 

 arrangement of the anal plates, from the other early Mono- 

 cyclica that they must be regarded as quite a separate family. 

 It is impossible to derive any of the other genera immediately 

 from them. This family — the Hybocrinidge of v. Zittel, as 

 emended by Wachsmuth and Springer — may therefore be set 

 on one side, and the course thus far cleared. 



The remaining Monocyclica of the Trenton are Ecteno- 

 crinus, Heterocrinus, locrinus, and Castocrinus. Of these 

 the last is obviously already much modified in the direction of 

 Proclivocrinus and Calceocrinus ; if the line along which the 



