ON VERTEBRA OF POLYPTYCHODOX. 43;j 



45. On an associated Series "of Cervical and Dorsal Vertebra of 

 Polyptychodon, from the Cambridge Upper Greensand, in the 

 Woodwardian Museum of the University of Cambridge. By 

 Harry Govier Seeley, Esq., F.L.S., F.G.S., &c, Professor of 

 Geography in King's College, London. (Read June 21, 1876.) 



The rarity of vertebrae of Polyptychodon in the Cambridge Green- 

 sand is out of all proportion to the relative abundance of teeth. In 

 the Woodwardian Huseum alone more than a hundred teeth are 

 arranged in illustration of the dentition of the genus, about half of 

 which (probably the remains of one animal) were found .at a Phos- 

 phatite washing on the Huntingdon Road. Many hundreds of 

 teeth have probably been collected, all in a state of black minerali- 

 zation ; and these can only be referred to several individuals. The 

 vertebrae collected do not appear to be the remains of more than two 

 individuals ; and these probably represent two species. They consist 

 of the bones so admirably described by Professor Owen in the 

 publications of the Palaeontographical Society for 1860, w T hich were 

 found near Haslingfield, and the associated series of remains from 

 the Huntingdon Road, belonging to a somewhat smaller animal, 

 catalogued at p. 45 of my ' Index to Aves, Ornithosauria, and Rep- 

 tilia,' which latter are the subject of the present notice. All the 

 vertebrae are in a condition of somewhat pale mineralization. I 

 mention this fact, because it is within my own knowledge that dif- 

 ferent parts of the same specimen are sometimes differently minera- 

 lized, and the condition has no importance as indicating a native or 

 derivative origin of the fossils. 



The Atlas and Axis. 



Professor Owen's figure represents the atlas and axis as being 

 more excellently preserved than they are, and as showing a clear 

 separation between the atlas and axis, which is not very definitely 

 marked in the fossil. 



The atlas and axis are preserved in the associated series, and show 

 no indication of consisting of separate bones — so perfectly are the 

 osseous elements blended — either where the external unarticular 

 surface is preserved or where the internal tissue is exposed by 

 abrasion. 



The extreme transverse width of the specimen is 5 inches ; its 

 depth from the middle of the neural canal is not more than 3^ 

 inches ; so that it is rather broader than the first specimen, and not 

 so deep. It shows no visible marks of compression, though it may 

 perhaps have been a little depressed. There are no traces preserved 

 of the neural arches. 



The anterior surface of the specimen is concavely cupped for the 

 hemispherical basioccipital ; but the cup is considerably abraded, 

 what remains of it being a circle of not more than 3 inches diameter. 



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