ON THE CLASSIFICATION OF THE LABYRINTHODONTS. 165 
IV. ATHROODONTA. 
Batrachiderpeton, Hancock & Atthey. 
Skull (figure). Wide; postero-lateral expansions large, produced far backwards ; 
maxillz deficient ; coronal bones defined by raised lines. Number of ossifications. 
No maxille; probably no jugals or quadrato-jugals. Orbits. Anterior, oval ?, 
large ?, incomplete, being bounded by bone upon the inner side only. Choana. Large, 
oval. Parietal foramen. Far forward, large, with raised margin. Teeth (disposi- 
tion). Premaxillary about 9 on each side, strong, equal ; palato-vomerine, a dense 
and large central mass of aggregated (vomerine ?) teeth, with a lateral (palatine ?) 
row in advance of the choana; mandibular about 16, in the anterior part only of 
each ramus. Teeth (structure). Conical, pointed, strong; striated and somewhat 
compressed towards the apex. Crunial sculpture. Tuberculate or rugose. 
Measurements (from Messrs. Hancock and Atthey’s Memoir), m 
Total length of skull ........ Soot b Sc bamconcuan doe ce carLoor 2:3 
Length of skull along middle line .......... cece eee eee e eens 1:875 
Greatest breadth: of Shall yes wey. « s seidisun wats a Felareld 0 sieve etajeye vlbrele e's 2°625 
Average length of premaxillary teeth ......... cece eee ee eee 06 
Average length of mandibular teeth ............seeeeeeeseeees 06 
B, rinEatuMm, Hancock & Atthey. 
Locality. Newsham (Northumberland). 
References. Hancock & Atthey, Nat. Hist. Trans. Northumberland and Durham, 
3 vol. iv. p. 208 [1871]. 
Pteroplax, Hancock & Atthey. 
Skull (figure). Spatulate, narrowed in front, with acute postero-lateral (epiotic) 
projections; occipital margin concave. Number of ossifications. There are appa- 
rently no maxill, lachrymals, prefrontals, postorbitals, jugals, squamosals, supra- 
temporals, or quadrato-jugals. Orbits. Large, anterior, incomplete, being bounded 
by bone upon the inner side only. Cranial sculptwre. Pitted, the intervening 
ridges imperfectly defined; irregular. Vertebre. Biconcave, thick, well ossified. 
The teeth and premaxilla described by Messrs. Hancock and Atthey as those of 
Pteroplax belong to Loxomma. 
Measurements. (From Messrs. Hancock & Atthey’s Memoir.) in 
Total length of skull (imperfect) 2.0... csccsewnsnevsvcercces 7 
Length of skull along middle line ....... cece cece tenet eens 3°75 
SUE earaee TEL, OLN ULG OTHE OLIN «chee, 5.10) ejainin sje se sie-s's 1+ « wlee/sial oleic (about) 1 
(From specimen in the Lecds Museum.) 
Greatest breadth of skull (along occipital margin) .............. 4 
Abernethy GOpIGME CONN UG </. -Sy0:0:<y0i 8 Aiare(et epotol oie oie's 4 haraity mol Palen reneets 1-75 
Antero-posterior depth (superficial) of largest vertebral centrum ,. —*45 
Greatest width of vertebral contrum .........s cece ec eenereees 1:3 
P. cornuta, Hancock & Atthey. 
Locality. Newsham (Northumberland). 
References. Hancock & Atthey, Nat. Hist. Trans. Northumberland and Durham, 
vol. iii. p. 66, t. ii. fig. 1, vol. iv. p. 207. 
[V. Uncharacterized. ] 
Pholidogaster, Huxley. 
Skull (figure). Imperfectly shown ; snout obtuse. Teeth. Two premaxillary teeth 
visible; these are conical, recurved, and strongly grooved at the base. Thoracic 
