28 Reports and Proceedings. 



This reptile was regarded by the author as foreshadowing the 

 form, of dentition that characterizes the existing group of Varanidce. 

 If the materials were at hand for a complete definition of its com- 

 parative osteology, Dakosaurus would probably exhibit a combina- 

 tion of Lacertilian and Crocodilian characters, but with the crodo- 

 dilian elements predominant. 



Discussion. —The President differed from the author as to the 

 conclusions he drew from the structure of the teeth. The teeth of 

 existing Crocodilia 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 Professor Owen in regarding Dakosaurus as Crocodilian rather 

 than Dinosaurian or Lacertilian. 



Mr. Wood Mason had seen in the Gavial of the G-anges, 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 the Anatomy of the test of AmpJiidetiis {Ediinocardium) 

 Virginianus, Forbes ; and on the genus Breynia." By P. Martin 

 Duncan, M.B., F.E.S., Sec.G.S., etc. 



After a careful examination of the Miocene AmpMdetiis from the 

 Virginian Tertiaries, the recent species of the genus from the Eu- 

 ropean and Australian seas were stated to form a group of very 

 closely allied forms. The Crag specimen of 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 a third-rate cha- 

 racter as regards structural importance ; and the author did not 

 consider that the genera EcMnocardium, Breynia, Lovenia, etc., had 

 a common origin, or that there was a close generic relationship 

 between them, because they had this fasciolar structure. He con- 

 sidered the fascicle to be an appendage to several generic groups 

 which were distinctly separated by other structural distinctions. 

 The result of an examination of the Nummulitic Breynice in the 

 Society's collection satisfied Dr. Duncan that there were only race 

 characters separating them from Breijnia Australiensis — a recent 

 Echinoderm. The persistence of these species, widely distributed 

 and of great geological age, was very remarkable. 



Discussion. — The President regretted, with the author, the pre- 

 vailing custom of determining species as much by their geological 

 position as by their structural affinities. He thought it was neces- 

 sary to have a knowledge of living forms, in order to estimate 

 correctly the value of the characters of extinct species. He con- 

 sidered that the presence of similar fascicles in different genera 

 might be explained in the opposite way to that which the author 

 adopted, and that they might be considered evidence of genetic 

 connexion, subsequent variations having produced differences of 

 generic value. 



