16 proceedings of the geological society. [nov. 25, 



Discussion. 



The President differed from the author as to the conclusions he 

 drew from the structure of the teeth. The teeth of existing Croco- 

 dilia had been but imperfectly described, and he thought he could 

 point out among existing Crocodiles teeth bearing the character 

 which the author regarded as Lacertilian. He agreed with Prof. 

 Owen in regarding DaJcosaurus as Crocodilian rather than Dinosau- 

 rian or Lacertilian. 



Mr. Wood Mason had seen in the Gavial of the Ganges, and in 

 the teeth of Teleosaurians from the neighbourhood of Oxford, the 

 same crenulations and compression, which he regarded as indicative 

 of a Lacertilian character. 



4. On tlie Anatomy of the Test of Amphidetus (Echinocardium) 

 Yirginianus, Forbes ; and on the Genus Breynia. By P. Martin 

 Duncan, M.B., F.E.S., Sec. G.S., &c. 



(This paper was withdrawn by permission of the Council.) 

 [Abstract.] 



After a careful examination of the Miocene Amphidetus from the 

 Virginian Tertiaries, the author regarded the recent species of the 

 genus from the European and Australian seas as a group of very 

 closely allied forms. The Crag specimen ot A. cordatus, described by 

 Forbes, could not be found ; but the examination of a series of recent 

 specimens decided that they were not specifically different from the 

 Miocene form. 



The unusual form of the ambulacral spaces, the nature of the 

 fascicle crossing them, and the resulting absence (more or less) of 

 pores within the fascicle were asserted to be of third-rate value 

 as regards structural importance ; and the author did not consider 

 that the genera Echinocardium, Breynia, Lovenia, &c. had a common 

 origin, or that there was a close genetic relationship between them, 

 because they had this fasciolar structure. He considered the fascicle 

 to be an appendage to several generic groups which were distinctly 

 separated by other structural distinctions. An examination of the 

 Nummulitic Breynice in the Society's collection satisfied Dr. Dun- 

 can that there were only race characters separating them from 

 Breynia Australiensis — a recent Echinoderm. The persistence of 

 these species, vridely distributed, and of great geological age, was 

 very remarkable. 



Discussion. 



The President regretted, with the author, the prevailing custom 

 of determining species as much by their geological position as by 

 their structural afiinities. He thought it was necessary to have a 

 knowledge of living forms, in order to estimate correctly the value 

 of the characters of extinct species. He considered that the presence 



