380 Mr. F. A. Bather on British Fossil Giinoids. 



ment may have arisen from the modified lateral arms of 

 Calceocrinus along lines similar to those followed in the 

 evolution of Crotalocrinus. The whole problem, however, is 

 one that, in the absence of more complete knowledge, admits 

 of much speculation but of no satisfactory solution. 



To pass to the Trenton Dicyclica — similar reasons cause 

 me to regard Merocrinus as the most ancestral of the 5 genera. 

 From Merocrinus, Ottawacrinus differs but little, and the two 

 were doubtless derived from a common ancestor of not much 

 earlier date. With this same ancestor Garabocrinus, though 

 an anomalous form, may have been closely connected. But 

 Dendrocrinus was probably derived more directly from Ottawa- 

 crimes, which, except in the development of a radianal, it 

 closely resembles. Euspirocrinus again shows, so far as the 

 arrangement of the anal area is concerned, a slight advance on 

 Dendrocrinus, from an immediate ancestor of which genus it 

 was probably descended. The arms of these genera resemble 

 one another in their simple dichotomy, and afford no evidence 

 either way. One thing is plain — Merocrinus, Ottawacrinus, 

 Dendrocrinus, and Euspirocrinus are all closely connected, 

 and are all primitive. Their exact relationships are of less 

 importance. 



Proceeding to the Niagara and Wenlock Limestones we 

 find, chiefly in the Old World, a great influx of new forms. 

 Thenarocrinus may be connected with Carabocrinus, but its 

 exact significance will be more fittingly discussed in a later 

 paper. Homocrinus very obviously carries on the line of 

 Dendrocrinus. Euspirocrinus of Gothland and Closterocrinas 

 of the Clinton group are direct descendants of the Trenton 

 Euspirocrinus obconicus, while Amplieristocrinus is a very 

 close relation. 



The four genera Streptocrinus, Arachnocrinus, Cyatho- 

 crinus, and Gissocrinus resemble one another in the presence 

 of a large brachianal in line with the radials, and in the 

 absence of a radianal. In this latter respect they differ from 

 all their contemporaries ; and here a moot point crops up : — 

 has the radianal become atrophied in Cyathocrinus, or was it 

 never developed? Messrs. Wachsmuth and Springer adopt 

 the former, 1 incline to the latter view. If my reading of 

 Ottawacrinus (PI. XIV. fig. 12) be correct, it is very easy to 

 derive Cyathocrinus and its allied genera from that genus 

 without supposing such a waste of force as the sudden growth 

 and more sudden disappearance of a radianal. The American 

 authors were evidently driven to their view by their belief that 

 the radianal was a primitive element of the dorsal cup. They 

 will perhaps point out that Botryocrinus and Sicyocrinus 



