PLETHODUS. Ill 



tubercles (fig. 10 a). The basicranial axis, so far as preserved (to the border of 

 the hyomandibular), is straight and parallel with the ridge of the cranial roof 

 behind the frontal angle. Its constitution is uncertain, but the greater part is 

 likely to be a parasphenoid (pas.), for from it there rises a low ridge of bone 

 uniting with an extensive laminar interorbital septum, which is probably an orbito- 

 sphenoid (os.). The supposed parasphenoid expands below the position of the 

 eye into a Plethodont plate ()>.), which is distinctly concave on its oral face. In 

 the mandibular suspensorium, the very deep and narrow hyomandibular (hm.) is 

 conspicuous, with a prominence on its thickened hinder border for the suspension 

 of the operculum. The metapterygoid, quadrate, and long slender ectopterygoid 

 with its minute teeth (ecpt.), are also seen in a plane external to the parasphenoid 

 dental plate in fig. 10. The articulation for the mandible seems to have been 

 beneath the middle of the orbit. The maxilla (fig. 10, mx.) is a deep laminar bone, 

 finely tuberculated at its oral margin, which forms the greater. part of the upper 

 border of the mouth. If it bore teeth, they must have been restricted to a tuber- 

 cular cluster on its inner face. The premaxillas are unknown, but may be fused 

 with the short ornamented rostrum, which curves inwards to the mouth below, and 

 seems to bear minute teeth. The mandible is short and very deep, the dentary 

 (d.) forming by far the greater part of the ramus. Its teeth are minute, obtuse, 

 and styliform, in more than one series, apparently forming a cluster. In one 

 specimen (fig. 10), displaced below the mandible, is a relatively large urohyal (uh.). 



Fig. 34. — Flops saurus, Linn. : about one ninth nat. size. — Existing in tropical seas. 

 After Jordan & Evermann. 



The operculum (op.) displays only radiating structural lines, but is evidently 

 incomplete in the fossils. The preoperculum (pop.) has a relatively large and 

 widely expanded lower limb (well seen in fig. 9 a). 



Horizon and Localities. — Zone of Holaster subglobosus .- Clayton, Sussex; 

 Dorking, Surrey; Bnrham, Kent. 



