y4 Mr. D. ]M. S. Watson on Pleurosaurus. 



freeing of the quadrate. The connection of the quadrato- 

 jugal with the parietal is for me a secondary condition 

 demanded for the efficient support of the quadrate. 



In the postcranial skeleton there is nothing to prohibit a 

 genetic connection with the Lacertia. 



The vertebra? are slightly biconcave and their arches and 

 centra correspond well enough with those of lizards. The 

 single rib-facet is carried on a short process at the suture 

 of the neural arch and centra^ some way behind the ante- 

 rior edge, exactly as in lizards. 



The ribs have a single expanded head, exactly as in 

 lizards. 



The limb-girdle and limbs, although modified for an 

 aquatic life, are quite Lacertiliau, as is the tail and so much 

 of the squ;imatiou as is known. 



In fact, the only character which is not thoroughly Lacer- 

 tilian is the presence of a complete plastron composed of 

 very delicate splints. This feature has in the past had a 

 very exaggerated importance attached to it, and the reduced 

 remnants of a plastron known in a recent lizard {Tiliqua) 

 shows that it cannot be held to invalidate the other very 

 striking resemblances. 



The -oldest definitely known lizard is Euposaurus thioUieri, 

 described by Lortet from the Lithographic Stone of Cirin, 

 and first recognized as a lizard by Boulenger. 



The small skull of PaUguana whitei from the Procolophon 

 beds (^Middle ? Trias) of Donnybrook, Upper Zwort Kei, 

 South Africa, seems to me to be not quite definitely deter- 

 minable. The specimen in its present condition agrees 

 exactly with Broom^s figures, but seems to me to give no 

 satisfactory evidence that the quadrate was really free and 

 that there was not a lower arcade, the anterior end of 

 which is, in fact, actually shown. When I examined the 

 specimen I was impressed by the resemblance of its quadrate 

 to that of Howesia, which is certainly no lizard. 



I think, therefore, that it is reasonable to regard Pleuro- 

 saurus (and Sauranodoii) as the little modified desceiidant 

 of the ancestral lizard stock, and that it may be put in a 

 special suborder of the Squamata, for which H. v. Meyer's 

 ordinal name Acrosauria may, perhaps, be used, of equal 

 value with the other suborders, Pytliouomorpha, Dolicho- 

 sauria, Lacertilia, and Ophidia. 



This view docs not necessarily conflict with that of 

 Williston, that Acrosceles is an ancestral lizard, althougii it 

 will necessitate slightly altering his views as to the mode of 

 development of the strcptostylic quadrate. Prof. Williston 



