48 



THE GEOLOGIST. 



therefore could not examine the locaUty where the Ammonites 

 are found, but which he infers, from information derived 

 from the natives, to be situated in black compact limestone 

 and earthy carbonaceous shales. 



3rd. — ^'Description of the remains of six species of Marine 

 turtle {Chelone) from the London Clay of Sheppy and Har- 

 wich. By Professor Owen^ F.R.S. 



Of the six sjDecies described, the remains of the first con- 

 sist of two specimens, one nearly a perfect cranium, and the 

 other a cranium with the carapace and plastron. The al- 

 most complete cranium wants only the occipital bone, and 

 presents a strong uninterrupted roof, extended from the pa- 

 rietal spine on each side, over the temporal opening; the 

 roof being formed chiefly by a great development of the pos- 

 terior frontals. This unequivocal testimony of the marine 

 genus of the animal is accompanied by similar evidence af- 

 forded in the large size and lateral aspect of the orbits, the 

 posterior boundary of which extends beyond the anterior 

 margin of the parietals ; by the absence of the deep emar- 

 gination which separates the superior maxillary from the 

 tympanic bone in fresh water tortoises, in the laterally ex- 

 panded spinous plate of the parietal bones being united by a 

 straight suture to the post frontals along three fourths of 

 its extent, and for the remaining fourth with the temporal 

 or zygomatic element ; and still further by the conformation 

 of the base of the skull. The lower jaw exhibits two proofs 

 of the marine nature of the turtle, the dentary piece forming 

 a larger proportion than inland or fresh water tortoises ; and 

 the under part of the symphysis being slightly excavated. 

 The outer surface of the carapace and plastron has the same 

 finely rugous character as that of the cranium. The cara- 

 pace is long, narrow and ovate, and is widest in front, ta- 

 pering towards a point posteriorly. It is not regularly con- 

 vex but slopes from the median line in tlie same manner as 



