FOSSIL VARANIDAE AND MEG AALNID AE. 
409 
admitted between the two mentioned species, as also pointed out by Mr. 
Siebenrock. It must not however be left out of consideration that within 
the same genus the humerus presents characters of comparatively trifling 
value as far as specific differences are concerned. A greater similarity 
among humeri does not therefore justify any conclusion to closer relation¬ 
ship. I n this case the humerus must be regarded as a tolerably 
indifferent component, of no especial moment, all the less as other mar¬ 
kings to which attention is drawn in the description concerning the 
vertebra of V. sivalensis, offer important differences between the 
Siwalik fossil and the recent «Kabara-Goya» (V. salvator LaurJ. 
Lydekker’s (1. c.) conclusion that «Since F. salvator is a coast-frequen¬ 
ting species it may, moreover, be not improbable that the Siwalik form 
was more closely allied to one of the smaller species now inhabiting 
the North-West Provinces and Punjab than the former», is to be regar¬ 
ded therefore as the unique, certainly very vague, statement with respect 
to the phylogenetical relations of the Siwalik Monitor. 
An examination of the vertebra of the Pliocene V. sivalensis 
Falc. in comparison to the same element of skeleton in the Pliocene- 
Praeglacia 1-N e o 1 i t i c • F. marathonensis reveals yet another fact 
worthy of notice. These tw r o forms, existing in the same epoch, the 
former in the East of Eurasia, the latter in the West, show far reaching 
dissimilitudes in the structure of the neural canal, a difference which 
might eventually prove to be of more general interest and signification. 
In my description of V. marathonensis I mentioned as a curious pheno¬ 
menon the large and massive construction of the vertebrae, presen¬ 
ting but a very narrow neural canal, smaller than in recent 
Monitors, as for instance in F. griseus Baud., the latter’s ver¬ 
tebrae being about twice as small as those of F. marathonensis, their 
neural canal being however only about as large as in the latter 
species. I tried to explain this fact by the process of desossification 
met with in most Holocene Vertebrates, and thus in Batrachia and 
Beptiles also, their Tertiary predecessors being characterized by a consi¬ 
derably robuster skeleton. Taking however into consideration that Palaeo¬ 
gene forms, such as F. Cayluxi for instance, bear markings agreeing through¬ 
out in this respect with the recent forms, the larger and ro¬ 
buster skeleton in Varanus cannot be regarded in gene¬ 
ral as an ancestral phenomenon. We are obliged to suppose 
that the ancient forms of Varanus (V. Cayluxi Filh., Varanus? Lemoinei 
Nop.j were only about of equal dimensions to our recent ones, and that 
increase in size followed later on, towards the beginning * 
of the N e o g e n e epoch. Thus would we have in this case an example 
