ICHTHY0PTERYG1A. 



quadrate by a foramen ; and the form and position of the stapes * 

 and columella. These conclusions are confirmed by the structure of 

 the palate. The absence of a lateral vacuity in the mandible is, as 

 was first pointed out by Owen, another character of the Ehyncho- 

 cephalia and Squamata ; while the backward position of the nares 

 is merely due (as in the case of the Parasuchian Crocodilia) to the 

 excessive development of the premaxillse. 



The Labyrinthodont features shown in this order, which are lost in 

 the other members of the Streptostylic branch, are the distinctness 

 of the lachrymal from the prefrontal, and the roofing over of the 

 infratemporal fossa by the separate squamosal and supratemporal. 



The distinct opisthotic is also a very generalized feature, at 

 present known elsewhere in the class only in the Chelonia, and 

 probably in Pariasaurus. The discoidal vertebral centra are also 

 markedly Labyrinthodont; but the transference of both costal 

 articulations to the centrum may be an adaptive feature. Miall 2 

 remarks on the resemblance of the pectoral girdle to that of the 

 Labyrinthodonts. 



Family ICHTHYOSAUKIME. 



All the known members of the'order are included in this family, 

 which is for the present taken to embrace the Baptanodontidce, 

 Ophihalmosauridce, and Mixosauridce of other writers 3 . 



Genus BAPTANODON, Marsh 4 . 

 Syn. Sauranodon, Marsh 5 . 



Distinguished from the following genus by the total absence of 

 teeth and of a dental groove in the jaws. 



Baur 6 has suggested that this genus is probably not separable 

 from the next, a view which was provisionally adopted by the writer 7 

 in a paper on the Ichthyopterygia. 



1 In Ichthyosaurus, the bone marked 4 in plate xxvi. of Owen's ' Liassic 

 Eeptilia' (Mon. Pal. Soc.), pt. 3 (1881). 



2 Rep. Brit. Assoc, for 1873, p. 241. 



3 See Baur, Amer. Nat. vol. xxi. p. 840 (1887). 



4 Amer. Journ. ser. 3, vol. xix. p. 491 (1880). 



5 Ibid. vol. xvii. p. 86 (1879). — Preoccupied. 



6 Bericht xx. Versamml. oberrhein. geol. Verein. p. 21 (1887). 



7 Geol. Mag. dec. 3, vol. v. p. 309 (1888). 



