Reports and Proceedings — Geological Society of London. 277 



II.— April 12, 1899.— W. WWtaker, B.A., F.R.S., President, in 



the Chair. 



Mr. A. M, Davies, in exhibiting a specimen of glauconitic lime- 

 stone from the Kimeridge Clay, said that it might easily be taken 

 for Upper Green sand. It came from a road-cutting near Wombwell's 

 Farm, Chilton (Bucks), about 40 feet below the top of the Hartwell 

 Clay, and therefore evidently from the true Kimeridgian. The 

 outcrop of the stone gives rise to a slight but distinct feature, 

 traceable for about \ mile along the hillside. There are traces 

 of fossils in the stone, but an impression of a biplex Ammonite 

 was alone recognizable. No similar bed had been previously 

 recorded from the English Kimeridgian. 



The following communications were read : — 



1. " Fossils in the University Museum, Oxford : I. Silurian 

 Echinoidea and Ophiuroidea." By Prof. W. J. Sollas, M.A., LL.D., 

 D.Sc, F.E.S. 



Attention is called to the correlation of structure and function in 

 the locomotive organs of Asterids, Ophiurids, and Echinids. In 

 the case of the two latter, movement depends on tension directed 

 along the tube-feet. In starfishes this tension is met by the dis- 

 position of the ambulacral ossicles in the form of an arch : in 

 urchins by a continuous tessellation of the surface, which would 

 only be weakened by arch-like interruptions. If, however, urchins 

 have been evolved from an Asterid stem, they may have originally 

 possessed arch-like ambulacral grooves, and the present plates 

 of the ambulacra may have been subsequently acquired. In 

 Palceodisciis ferox of the Lower Ludlow, Leintwardine, which 

 by the structure of the buccal armature is definitely shown to 

 have been an Echinid, the ambulacra possess just such characters as 

 theory anticipates : an inner arch of poriferous ambulacral plates, 

 homologous with those of a starfish, is closed externally by a 

 series of paired plates, which represent the ambulacral series of an 

 urchin. 



The undoubted Asteroid affinities of the urchin lead to an 

 attempt to find homologies for the elements of ' Aristotle's Lantern ' : 

 the pyramids are regarded as equivalent to the first pair of adambu- 

 lacral plates, the epiphyses to the corresponding pair of ambulacral 

 plates of the Echinoid series, and the teeth are compared to the 

 Asteroid odontophore, which has acquired a persistent root. 



A new genus assigned to the Echinida is characterized by the 

 excessively numerous minute plates which form the interambulacra. 

 Keference is made to Echinocystis pomum, Wyv. Thomson ; and to 

 a species of Protocidaris, Whidborne, from Lower Ludlow beds, 

 which seems to be identical with the type species found in Devonian 

 rocks. 



The results are given of a re-examination of the unique specimen 

 on which Dr. H. Woodward founded the genus PJucladia. The author 

 agrees with Dr. Woodward in regarding the exposed surface of this 

 fossil as ventral ; it bears the buccal armature and madreporite, 



