Geological Society. 183 



which, interradial in position, are much more prominent than the 

 rest. So far as is yet known, these features occur in no other 

 recent Comatula, with the exception of one species from the South 

 Pacific, in which there is a faint indication of such ribs, but they 

 are all equal. Another Antedon-s\iecies is described from the Chalk 

 of Sussex. It differs from Antedon paradoxa in the absence of these 

 ribs, and in the shallowness of the centrodorsal cavity. 



Two species are described from the gault of Folkestone. One is 

 an Antedon with no special relations to any recent forms. It might 

 have lived as well at 20 as at 500 fathoms. But the other species 

 is an Actinometra, possessing certain characters only known to 

 occur in species from quite shallow water, 20 fathoms or less, in the 

 Philippine Islands and Malay archipelago. The centrodorsal is a 

 flat plate, nearly on a level with the surface of the radials, or some- 

 times even below them, separated from them by clefts at its sides, 

 and entirely devoid, not only of cirri, but also of cirrus-sockets. 

 This condition is only an extreme stage of the metamorphosis of the 

 centrodorsal piece, which bears cirri for a time after its liberation 

 from the larval stem ; but these cirri eventually disappear, and 

 their sockets become obliterated. The ' Challenger ' collection 

 contains a series of specimens of Act. Jukesii from Torres Straits, 

 which illustrate this point very completely ; and it is therefore of 

 no small interest to find a fossil Comatula which shows one of the 

 extreme stages of the metamorphosis. 



The large size of the three Antedon-species from the Chalk and 

 Gault is very remarkable. Ant. paradoxa has a centrodorsal half 

 as wide again as that of any recent form ; while Ant. Eschrichtii 

 is the only recent species with a centrodorsal approaching the size 

 of those of the other Chalk Antedon and of that from the Gault. 

 Act. Loveni from the Gault, however, and the older Comatulae, all 

 had small calices like most recent species. An elegant centro- 

 dorsal (Ant. rotunda) is described from the Haldon Greensand, and 

 also two species from the Bradford Clay. One is an Antedon, the 

 oldest known, with no special characters ; the other is an Actino- 

 metra, with a centrodorsal essentially like those of species now 

 living in shallow water in the Philippines and Malay archipelago. 

 The oldest known Comatula, an Actinometra from the Bath Oolite, 

 has similar relations. 



December 17, 1879.— Henry Clifton Sorby, Esq., L.L.D., F.R.S., 

 President, in the Chair. 



The following communications were read : — 



1. "A Contribution to the Physical History of the Cretaceous 

 Flints." By Surgeon-Major G. C. Wallich, M.D. 



The author described the origin, the mode of formation, and the 

 cause of the stratification of the Chalk flints. Taking as the basis 

 of his conclusions the fact brought to notice by him in 1860, namely 

 that the whole of the Protozoan life at the sea-bed is strictly limited 



13* 



