eS Sees err th 
pe eS 
ON THE CLASSIFICATION OF THE LABYRINTHODONTS. 163 
Measurements (from Messrs. Embleton and Atthey’s Memoir and Plates), 
in. 
Margen othyopslcmllpes.. wet crasgidleds «4 ave siasunbia ole garelele (about) 13-5 
Length of skull along middle line ......... eee eee ec even eee enes 115 
Greatest breadihot Gull). .:..5 - lacie aitielareie javeyols ee clebie ee wesiarearen 8 
PPC R CGD. 8 ATA! OF OFDILS 0! «sna: 2°45. dinjnie 8! Reins aye 0, nae 0; le) (about) 6 
From centre of occiput to posterior end of orbit ......... ee eeeee 25 
From tip of snout to anterior end of orbit............. eee eens 5 
MS HL Ol ONO tiga ah ey Sciety chia by vids & 1s) aH PO GEOR: Sanlah Jolove\eyoreragarecod yrs.» 4:5 
Sober ae Fea chia ET Ctae rat eto sy atcha lone ove) < yes: 50: enerat sear emelptoketelal © gigi oligo iq: #feuaters)s 15 
cant wren Of nterorbital Space... i,.s,.4 5 csisiy eetien «+e clepeeie ae ® 15 
Distance between external nasal foramina.......... eee eee eens 2-76 
From tip of snout to external nasal foramen.........+.esee renee 2 
Prentestdepuln of mandible .'!.’.’./:0's wecges res qyocuccls me hana 2°75 
Extent of mandibular symphysis ........0cessececcseeceewoes 175 
Diameter of largest palato-vomerine tusk (longitudinal).......... 7 
Rs * A (irensyerse) lees vel m3) 
Antero-posterior depth (superficial) of largest vertebral centrum .. 65 
Greatest width of vertebral centrum ..........cce eee e ener cee 13 
Length of longest rib preserved ...........005 Shi Get RIE OR © or 809 
L. Auimant, Huxley. 
Locality. Edinburgh, Glasgow, Newsham, Broseley, Longton. 
References. Huxley, Q. J. Geol. Soc. vol. xviii. p. 291 [1862].—Hancock & 
Atthey, Trans. Nat. Hist. Soc. Northumberland and Durham, vol. iv. pp. 
201, 390 [1871].—Embleton & Atthey, Ann. Nat. Hist. ser. 4, vol. xiv. 
p. 38, pls. iv.~vil. [1874]. 
Zygosaurus, Eichwald. 
Skull (figure). Triangular, with concave sides and obtuse snout ; occipital border 
concave; skull lofty in the occipital region, falling away gradually in front and 
rapidly on the sides. 
Hichwald remarks that “the skull is distinguished by large temporal grooves, 
similar to those of the Crocodilian Sauria, which serve for the reception and attach- 
ment of the temporal muscles. These are observed in the Labyrinthodonts also, 
but especially in the Enaliosauria, as in Nothosaurus and Simosaurus. Thus 
Zygoscurus in this respect connects the Labyrinthodonts with the Hnaliosauria and 
Crocodilia” *. 
It does not, however, appear that Zygosaurus is fairly comparable as to the tem- 
poral region of the skull with Crocodilia. It has doubtless wide postorbital depres- 
sions, which probably served for muscular attachment; and these depressions may 
have been destitute of sculpture, though in the only skull known the original sur- 
face of this and other parts has been removed by fracture. The sutures are effaced, 
and it is therefore impossible to say positively whether the supratemporal and post- 
orbital ossifications, which best distinguish the upper surface of the Labyrinthodont 
from that of the Crocodilian skull, were present in Zygosawrus or not. Probably 
they were, and the temporal depressions of Zygosawrus would in this case much 
resemble those of Loxromma. There is only a distant similarity between the shallow 
postorbital grooves of Zygosaurus and the vacuities circumscribed by bone which 
occupy a large part of the temporal region in Nothosaurus and Simosaurus. Eich- 
wald’s remarks may refer to the depressions in the occipital tract of the skull, 
though nothing quite similar is found in recent Crocodilia. The state of the speci- 
* “Der Schidel zeichnet sich durch grosse Schlafengruben aus, die in ahnlicher Ent- 
wicklung in den krokodilartigen Hidechsen zur Aufnahme und Befestigung der Schlafen- 
muskeln dienen, und auch in den Labyrinthodonten, vorziiglich aber in den Enaliosauriern, 
wie im Nothosaurus und Simosaurus beobachtet werden, so dass der Zygosaurws hierin die 
Labyrinthodonten mit den Enaliosauriern und Krokodiliern verbindet.’’—Bull. de la Soc. 
des Naturalistes de Moscou, tom. xxi. (1848), p. 159. 
; mu 2 
