PROF. H. G. SEELEY ON PSErnOPIIORTJS POLIGONUS. 413 



ing my attention to this remarkable specimen; to Director von Hauer, 

 not only for facilities afforded me in studying the specimen, hut for 

 the beautiful photographs which accompany my paper ; to Dr. 

 Giinther, of the British Museum, for the opportunity of demonstra- 

 ting its affinities with SjpJiargis by studying the skeleton of that type ; 

 and to the Council of the E-oyal Society for assistance in investigating 

 this type in a distant locality. 



EXPLANATION OF PLATE XV. 



(Figures half the natural size.) 



Fig. 1. Portion of dermal shield of Psepkophorus poly ff onus, Yon Meyer, showing 

 part of an elevated longitudinal keel with polygonal plates on each 

 side of it, which differ in form and size and mostly show a superficial 

 radiated ornament. Beyond the point where the figure 1 is placed, the 

 slab shows thin plates with a smooth surface, which may be marginal. 

 2. Vertebra from the under side of the slab, probably cervical, fractured 

 longitudinally and imbedded in the matrix, a. The anterior cup. b. 

 The posterior ball. c. A fragment of the neural arch blended with 

 the centrum, d. Transverse process of the right side, imperfect, 

 but directed outward and upward. 



DiSCirssiON. 



Mr. Htjlke agreed with the view taken by Prof. Seeley of the 

 specimen. As to the classification proposed, it would require careful 

 consideration. 



Prof. Dtjncan said the possible existence of something like ribs 

 in the cervical region was interesting. The position of the shoulder- 

 girdle in the Chelonians was always a difficulty. This, however, 

 might have been gradually assumed during the early stages of life ; 

 but the presence of cervical ribs rendered the former existence of 

 the scapula outside the dorsal ribs and in front very difficult of 

 comprehension. The classification of the Chelonians was at present 

 in great confusion. He thought there was much to be said for 

 the simplicity of Prof. Seeley's classification. 



The President asked whether these dorsal-shielded forms preceded 

 the others in time or not. 



Prof. Seeley said the specimen was Pliocene, i. e. the newer di- 

 vision of the Tertiary. It comes from Neudorfl, near the borders 

 of Hungary and Austria, and is associated with Manatees and Che- 

 lonians of ordinary type. It has been compared by von Hauer with 

 Psephoderma alpina from the Trias in the Munich Museum. This 

 specimen he had seen, which he thought was n6t a Chelonian, 

 though it might be an antecedent form or even a fish, like Ostracion. 

 It was curious that the Mesozoic Chelonia belong, so far as known, 

 to those with well-developed carapaces ; but he thought that Sjihargis 

 was nevertheless the more primitive type. 



