Geological Society. 4 1 5 



in individuals of the fullest growth and largest size, evincing a very 

 languid circulation in this family of reptiles. The atlas and axis of 

 Ichthyosauri, the author states, are usually found adhering together, 

 the connexion between them being so intimate that it is rarely pos- 

 sible to disunite them ; and when this has been effected, the surfaces 

 have borne the appearance of fracture more frequently than that of 

 natural division. In one instance in which he succeeded in separating 

 the two bones, the articulating surfaces were nearly even, and with- 

 out cup. This union of the two vertebrae appears to have received ad- 

 ditional strength from a small bone which articulated with the under 

 circumference of the atlas and axis, showing, as the author observes, 

 that in the anterior region of the spinal column strength and not la- 

 titude of motion was required. This bone is a nearly circular, solid, 

 umbonated disc ; the central projection being on the inferior or ex- 

 ternal surface, while the upper is depressed anteriorly and posteriorly 

 for the purpose of articulating with the atlas and axis, the two sur- 

 faces being divided by a transverse elevation corresponding with the 

 line of union of the vertebrae. The atlas and axis have their circum- 

 ferences prolonged in the form of two tangents meeting at an obtuse 

 angle on the under surface. These processes are truncated, and form, 

 when the vertebrae are in apposition, a triangular depression for the 

 reception of the two articulating surfaces of the interspinous bone. 

 Sir Philip Egerton states that Mr. Owen has informed him, that a 

 bone somewhat analogous in position, although not in form, occurs 

 in some recent saurians. The apparently two succeeding vertebrae 

 present, at the lower part of their articulating surfaces, an alternating 

 elevation and depression, fitting into each other so exactly, as to limit, 

 to a great extent, the motion between the bones. Some of the other 

 cervical vertebras are also remarkable for the flatness of their surfaces, 

 the intervertebral cavities being nearly obliterated. In conclusion, 

 the author says, that the conditions under which the atlas and axis 

 are found j the existence of an auxiliary bone connecting the two ; 

 the form of the articulating surfaces of the cervical vertebras, and the 

 consequent contraction of the intervertebral cavities, all tend to prove 

 that the extent of motion in the cervical region of Ichthyosauri was 

 extremely limited, at the same time that its strength was propor- 

 tionally increased. 



May 27th. — A paper was first read, " On certain Lines of Eleva- 

 tion and Dislocation of the New Red Sandstone of North Salop and 

 Staffordshire, with an account of Trap Dykes in that Formation, 

 at Acton Reynolds, near Shrewsbury;" by Roderick Impey Mur- 

 chison, Esq., V.P.G.S. 



The author refers to former memoirs, read before the Society, in 

 which he pointed out the existence of certain bedded trap rocks, in- 

 terstratified with transition deposits, and of other intrusive trap rocks 

 which have been subsequently injected amid these stratified masses. 

 The Breiddin Hills, west of Shrewsbury, afford examples of both these 

 classes of trap rock, in ridges running from west-south-west to east- 

 north-east, and also indicate, upon their flanks, that elevatioos have 

 taken place along these lines, subsequently to the deposition of the 



