Geological Society of London. 323 



Prof. T. Eupert Jones stated that in the Carboniferous limestone the Cypridinidae 

 frequently occur in layers, hut he thought these were deposited at no great depth, 

 probably not more than 100 fathoms. The greatest depth from which he had seen 

 Entomostraca from, the Atlantic was upwards of 1000 fathoms. These, however, 

 belonged to different genera from those which he had been describing. Their modern 

 congeners, though mounting to the surface in the evening, no doubt descended to 

 considerable depths during the day. 



(2).— May 14th, 1873.— Joseph Prestwich, Esq,, F.E..S., Vice-President, in the 

 Chair. — The following communications were read : — 1. " On the genus Palceocoryne, 

 Duncan and Jenkins, and it Affinities." By P. Martin Duncan, M. B. Lond., F.R.S., 

 V.P.G.S., ProL of Geology in Eling's College, London. 



In this paper the author referred to certain minute fossils from the Carboniferous 

 rocks of Scotland, described by himself and Mr. Jenkins in a paper read before the 

 Eoyal Society, as belonging to the Hydroida, and most nearly resembling the recent 

 genus Bimeria, Wright. He stated, that numerous specimens since received from the 

 Geological Society of Scotland threw some further light on the nature of these fossils, 

 and showed especially that in all probability the base is not really cellular, but that 

 the cellular appearance is produced by the growth of the real base of the polype over 

 the cells of the Fenestella on which it grows. The author further described what he 

 believed to be the mode of growth of this organism, as displayed in the new specimens. 



2. " Notes on Structure in the Chalk of the Yorkshire Wolds." By J. R. Mortimer, 

 Esq. Communicated by W. Whitaker, Esq., F.G.S. In this paper the author de- 

 scribed a peculiar structure observable in chalk from Yorkshire and elsewhere, giving 

 it a striated appearance. This structure had been ascribed by Dr. Mackie and others 

 to slickeusides. The author adduced reasons for doubting the mechanical origin of 

 these striations, and argued that they are of an organic nature. He ascribed them to 

 corals, and remarked that similar striae occur in all limestone formations. 



Discussion. — Prof. Duncan, though differing entirely from the author, had been 

 struck with the reasons which he had for his surmises. He exhibited some speci- 

 mens of recent West-Indian Corals, which offered at first sight much resemblance to 

 the character shown in the Chalk. It was to be observed that no reef-building corals 

 are occupants of the deep seas, in which there is httle doubt the Chalk was deposited. 



Mr. H. Woodward thought that in one or two instances apseudomorph of a Sipkonia 

 might be discerned. He could not, however, accept the fibrous structure as organic. 

 It appeared to him to result from mechanical causes. 



Mr. Whitaker read a note from Mr. Judd, who held that these specimens were not 

 due to any organic origin. The quasi -crystalline structures known as "cone-in- 

 cone," or " beef," seemed to him closely related ; and in the Yorkshire Chalk an in- 

 cipient crystallization of this kind had been set up ; and the fact of its existence sub- 

 sequently developed by the solvent action of the water, without which it might have 

 remained latent in the body of the Chalk. In one instance the fibrous structure of a 

 portion of the shell of an Inoceramus was continuous with that of the matrix. Mr. 

 Whitaker was glad that the author had called attention to the subject, and thought 

 that all would go with him in doubting that the structure was due to slickensides. He 

 mentioned the presence of similar strise in the Chalk of Surrey. Another observer had 

 called attention to the greater abundance of the markings in the neighbourhood of 

 fissures than in the solid Chalk. 



Mr. Evans mentioned the occurrence of similar structure in the Chalk of Hertford- 

 shire. The portions of the rock in which it occurred are usually harder than the 

 surrounding rock ; and in some cases the structure might be seen to pass into that of 

 the ordinary chalk. He considered it to be mainly due to chemical causes. 



The Chairman suggested the desirability of analysis to determine whether there 

 was any difference in the chemical constitution of the fibrous and non-fibrous chalk. 



Mr. Forbes, referring to the possibility of this structure being due to crystallization, 

 thought its occurrence in the harder parts of the chalk in favour of this view ; chalk 

 being a nearly pure carbonate of lime, might crystallize either as calcite or aragonite. 

 The specimens in question showed no trace of the peculiar cleavage of calcite, but 

 had a strongly developed fibrous structure resembling aragonite ; and as this mineral 

 is the most instable form of crystalline carbonate of lime, it would account for its 

 subsequent amorphous condition. He thought as these specimens were more com- 

 monly found near joints, that pressure had also assisted in rendering this structure 

 more visible, and that the structure itself might be accounted for by a combination of 

 the forces of crystallization and mechanical pressure. 



3. "On Platysiac/um sclerocephalum and Palmospinax priscus, Egerton." By Sir 

 Philip de Malpas Grey-Egerton, Bart., M.P., F.R.S., F.G.S. The two species of 

 fossil Fishes noticed in this paper were described by the author in the 13th Decade of 

 the Memoirs of the Geological Survey, published in 1872. They are both from the 



