248 STEEPTOSTYLIC BRANCH. 



The following specimens were obtained from the Middle Purbeck 

 of Durdlestone Bay, JSwanage, Dorsetshire, and belong to the 

 BecMes Collection. Purchased, 1876. They include the types. 



48209-12. Four fragments of the maxilla. Figured by Owen in his 

 {Fig.) ' "Wealden and Purbeck Eeptilia ' (Mon. Pal. Soc), pt. v. 

 pi. viii. figs. 1-4 (1861). 



48213. Portion of the dentary bone. Figured, op. cit. fig. 5. 



(■%•) 



48214. The imperfect right dentary, with the crowns of the teeth 

 (Fig.) broken off. Figured, op. cit. figs. 6-8. 



48215. The two imperfect dentary bones. The right is figured 

 (Fig.) (reversed), op. cit. fig. 9. 



STEEPTOSTYLIC BEANCH. 



The four orders included (after Baur l ) in this branch may be 

 collectively characterized as follows : — 



Dentition usually acrodont or pleurodont, and in the adult the 

 teeth anchylosed to the bone, but the teeth may be implanted in a 

 groove without anchylosis ; teeth not unfrequently present on the 

 palatine and pterygoid, and more rarely on the vomer 2 . Fre- 

 quently a parietal foramen ; superior temporal arcade generally 

 present, inferior present or absent ; quadrate movably or immov- 

 ably articulated by its proximal extremity ; a columella (epiptery- 

 goid) generally present. Limbs absent in some cases. Precoracoid, 

 when present, anchylosed to coracoid (fig. 52). A T-shaped inter- 

 clavicle and clavicles present in those terrestrial forms which have 

 limbs, except the Ehiptoglossa. Generally all, or nearly all, the 

 dorsal ribs articulating by single heads ; dorsal vertebrae either with 

 short or rudimental transverse processes, which (with the possible 

 exception of the Proterosauria) are never placed entirely on the 

 arch, or (Ichthyopterygia) with a pair of facets on the centrum ; 

 with one exception 3 , not more than two vertebras in sacrum. 

 Abdominal ribs present or absent. Humerus generally with entepi- 

 condylar foramen. In terrestrial pentedactylate forms the number - 

 of the phalangeals is 2, 3, 4, 5, 3 in the man us, and 2, 3, 4, 5, 4 

 in the pes. There is never a lateral vacuity in the mandible. 



1 Biol. Centralblatt, vol. vii. p. 486 (1887). The Ichthyopterygia will come 

 in Part II. of the present work. 



2 Among recent forms in some Anguidce and the young of 

 8 Proterosaurus linlti, Seeley, Phil. Trans, 1887, p. 201. • 



