74 Geological Society: — 



curve as the older rocks, and broken through, nearly in the centre 

 of the curve, by the basaltic cone of Nga Tutura. This volcano is 

 about 600 feet high, and is chiefly composed of basaltic lava-streams, 

 with but little tuff. The eruption is considered by the author to 

 have been submarine. 



Capt. Hutton then stated his conviction that the fluid matter 

 which escaped was not connected with a central molten interior of 

 the earth, but was derived from rocks not much more than 1000 

 feet in depth, and that the synclinal in question was caused by a 

 subsidence into the cavity thus formed. 



3. " On Dalcosaurm." By J. Wood Mason, Esq., F.G.S. 



The Kimmeridge Clay of Shotover Hill has yielded five specimens 

 of the teeth of this reptile, now for the first time represented, as a 

 British genus. After noticing the bibliography of the subject, and 

 the presence of specimens in various museums, the author proceeded 

 to describe the characters of the teeth. They are large, conical, 

 incurved, and slightly recurved, having two sharp, prominent, cre- 

 nulatcd, longitudinal ridges, which are situated midway between 

 the convex and concave curvatures. 



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, Dahosaurus would probably exhibit a combina- 

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

 dilian elements predominant. 



The Peesident 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 Dahosaurus as Crocodilian rather than Dinosau- 

 rian or Lacertilian. 



4. " On the Anatomy of the test of AmpMdetus (Ecliinocardiimi) 

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

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



After a careful examination of the Miocene Ampliidetus 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 ambulacra! spaces, the nature of the 

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

 pores within the fasciole, were asserted to be of a third-rate cha- 

 racter as regards structural importance ; and the author did not 

 consider that the genera Echinoeardium, Breynia, Lovenia, &c. 

 had a common origin or that there was a close genetic relationship 

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



