VERTEBRATES. 137 



This animal combines with its Batrachian a few Lacertilian characters, having 

 some resemblance to Dawson's genus Hylonomus, and much affinity with Prof. 

 Wyman's Raniceps Lyellii. Its squamous integument and narrow nasal roof 

 give it the somewhat Lacertilian physiognomy, more especially Gcccotian, in 

 its broad cranium and orbits, its large marginal palpebral scales, and rather 

 short digits. Its true affinities are indicated by the presence of two premaxil- 

 laries, with a squamoso-postorbital arch, as in Labyrinthodontia. some Batrachia 

 Gradientia, and Crocodilia ; its quadratojugal arch, as in Labyrinthodontia and 

 Batrachia Salientia.; its posteriorly directed oblique quadratum and lack of 

 ribs, as in Batrachia Salientia; its probably short pelvis, short separate bones 

 of the leg and fore-arm ; its opisthocselian dorsal vertebras, and long caudal 

 neural spines, as in Batrachia Gradientia. It is then the type of a group inter- 

 mediate between the Labyrinthodontian and Gradient Batrachians, distin- 

 guished from the former by the opisthocaelian vertebrae, absence of ribs, and 

 pleurodont dentition; and from the latter by the scaly integument, absence of 

 ribs, and structure of the nasal and pre-frontal regions. But one genus of 

 Salamanders, Glossolega, has a similar os fronto-squamosal or posterior zygo- 

 matic arch. A ribless type might, however, well exist among Gradientia, when 

 we consider the great difference between their development in Pleurodel.es on 

 the one hand, and Amphiuma on the other. From the Salientia the dentige- 

 rous mandible, squamosal arch, form of vertebrae, sacrum and extremities, etc , 

 widely distinguish it. To the Batrachian orders Labyrinthodontia, Gradientia, 

 Gymnophidia and Salientia, the present may be added, under the name Xen- 

 orhachia. 



The general form of the skull is much that of a frog, and large in proportion 

 to the size of the animal ; its length is one-half that of the spinal axis from the 

 occiput to the middle of the sacral region, and five-sixths its own breadth in 

 the flattened specimen. The outline is not broadly rounded, as is usual among 

 Salamanders, but is slightly contracted, as in many frogs. The orbits are 

 large, regularly rounded their longitudinal diameter one and one-half times the 

 frontal width ; their point of nearest approach is behind, opposite the position 

 of the iris; one diameter, measured obliquely in advance of each, extends a 

 little beyond the common premaxillary suture. 



The premaxillary bones have considerable horizontal extent, terminating 

 opposite the narial openings, each bearing eleven or twelve teeth. Their nasal 

 spines were in close contact, and do not appear to be prolonged backwards, as 

 in most Gradientia. The external nares are rather widely separated, as in 

 most Gradientia, the integument, which they pierced, roofing a large space 

 between the median and peripheric bones of the muzzle. The roof of the nasal 

 cavities is a truncate cuneiform plate, whose apex joins that of the premaxil- 

 laries. Its composition can only be conjectured, from the appearances pre- 



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