Osteology of Loxomma Allmanni. 61 



The skull of Loxomma has two pairs of bones that are 

 wanting in Fishes and in the Crocodilia, namely the postorbital 

 and the supratemporal ; these contribute much to enhance both 

 tlie length and the breadth of the cranium ; they are present, 

 however, in the Ganocephalous Dendrerpeton and Archego- 

 saurus, in the Labyrinthodontia, and in the Ichthyopterygia ; 

 but the general ossification of the skull is much further 

 advanced and consolidated in Loxomma than in these other 

 animals, whilst in Archegosaurus, at least, it is very incom- 

 plete, having "been chiefly active at the surface" (Owen, 

 Pala3ont. p. 195). 



Besides the above two pairs of bones there is in Loxomma, 

 as in Ar'chegosauruSj another pair, to which attention was 

 called above in the description of the bones, and which lies 

 between the parietals in front and the occipital vertebra 

 behind. This pair is called by Owen, Huxley, and Von 

 Meyer " supraoccipital." 



Now, in Loxomma at least (though not in Archegosaurus, 

 on account of incomplete ossification) the occipital vertebra is 

 formed by the basi- and exoccipitals and a fourth piece of tri- 

 angular form which is the keystone of the arch, and which in 

 consequence we have called the true supraoccipital : the same 

 arrangement exists in the skulls of Crocodiles and Alligators ; 

 and in these the occipital vertebra so constituted articulates 

 above with the posterior borders of the parietals, and is more 

 or less overhung by them ; but in Loxomma the pair of bones 

 above mentioned is interposed between the arches of the 

 parietal and occipital vertebrge, projecting beyond and over- 

 hanging the occipital vertebra exactly as the parietal arch 

 does in Crocodiles &c. 



Is this pair of bones properly designated supraoccipital, 

 though it is actually so in position ? Does it belong at all to 

 the occipital or to the parietal vertebra, or is it a pair of 

 dermal bones intercalated between the arches of these two ? 

 If it belong to the occipital, then there are three supraoccipitals ; 

 if to the parietal vertebra, then this must have had four pieces 

 forming its arch. It seems most probable that it belongs to 

 neither, but is a pair of independent pieces like the post- 

 orbitals (if these are not merely subdivisions of the postfrontals) 

 and the supratemporals, and, like them, dermal ossifications, 

 and let in, so to speak, between the regular vertebral arches. 

 They cannot be the paroccipitals of Professor Owen. 



That Loxomma had limbs, probably four, in the form of 

 paddles, there can be little doubt ; but they were probably not 

 very large or strong ; their digits were perhaps not more 

 than four in number. The length of our Loxomma cannot 



