1904.] NATURAL SCIENCES OP PHILADELPHIA. 469 



the Rocky mountains, but if the view of Dr. Baur be accepted, that the 

 gradual disappearance of the quadrato-jugal is a progressive character, 

 T. major of the southern Austroriparian and T. hauri of Florida are 

 the most primitive. 



A distinctly negative character of the whole Atlantic subregion 

 is its poverty in lizards, their almost complete absence being, in fact, 

 the correlative of an abundance of water turtles. Its lizards are So- 

 noran, with the exception of Ophisaurus, restricted to the Austro- 

 riparian, whose close relationship to the Palsearctic Pseiidopus justifies 

 placing its original centre along the Atlantic coast, and Rhineura, now 

 only found in Florida, but perhaps known from the Oligocene of Da- 

 kota. Ldolepisma laterale, which occupies only the Austroriparian 

 and the southeastern corner of the Eastern as far as New Jersey, 

 belongs to a genus of wide extension in the Austrahan, Ethiopian and 

 Oriental regions, but having no other representative in the Holarctic 

 except one in China, whose specific characters are identical with it.^ 

 This instance conforms to the unknown law which has preserved 

 on the eastern shores of Asia and North America so many allied rem- 

 nants of ancient groups among both animals and plants. 



More exact e\'idence is afforded by Ophidia, for with two exceptions 

 it is believed that the genera now widely spread in the Nearctic can 

 be shown to have probably originated in the eastern centre. Of those 

 more locally restricted, which must in most cases be descendants of 

 these earlier forms, a difficulty must be admitted in the comparative 

 absence of structural clues to relationship, especially in Colubridge. 

 The relative position assigned to genera by Mr. Boulenger, however, 

 merits a high degree of confidence and has been much relied upon. 

 It may be added that there are quite enough cases where high proba- 

 bility can be assm-ed, to warrant propositions with which the uncertain 

 ones at least fail to conflict. 



The genus Tropidonotus, cosmopolitan as to the greater life areas 

 except that it enters only the northern border of the Neotropical, in 

 the Nearctic is absent from the Pacific coast, and in fact enters the 

 Sonoran only by its river bottoms, from which the assumption is 

 justified that it originally entered North America from western 

 Europe. The common species of the whole Atlantic subregion, 

 Tropidonotus sipedon, seems quite surely to have been near the parent 

 form, though it is less clear which of the two subspecies, T. s. sipedon 

 or T. s. fasciatus, should be regarded. The young of both, as a rule. 



3 Boulenger, Cat. of Lizards, Vol. Ill, p. 264. 



