FOSSIL AND RECENT 



169 



portion ' of the pterotic (p. 156) nor a foramen between the supraoccipital and 

 epiotic could be identified in A . oweni. 



The depth of the neurocranium at the autosphenotic spine is relatively greater in 

 A . oweni than in A . vulpes. The lateral neurocranial wall of A . oweni is incompletely 

 known from a single specimen, and comparison with the extant species is difficult 

 as features of individual variation cannot be taken into account. However, a few 

 remarks are necessary. 



The region which is occupied by the saccular swelling in A. vulpes is depressed 

 and perhaps represents the point to which an arm of the swimbladder reached. In 

 A. vulpes the swimbladder diverticulum, although of variable development (Green- 

 wood 1970a), never reaches as far forwards as this point. 



The subtemporal fossa of A . oweni is considerably larger than in A . vulpes and a 

 horizontal ridge forms its ventral border. In A. vulpes no such ridge exists. 



The posterior opening of the jugular canal (pars jugularis) lies, as usual, within 

 the prootic bone, but in A. oweni the opening is situated far forwards, whereas in 

 A. vulpes it is close to the posterior margin of the prootic. The specimen of A. oweni 

 shows a lateral bridge of bone spanning the jugular groove behind the posterior 

 opening of the pars jugularis. A greater anterior development of this lateral bridge 

 would eventually meet the lateral commissure and produce the same spatial rela- 

 tionship of the posterior opening of the jugular canal as in A. vulpes. This develop- 

 ment of a bridge, which may otherwise be thought of as a fenestrated lateral 

 commissure, is in all probability subject to individual variation. 



Lying antero- ventral to the posterior opening of the pars jugularis is a large 

 postero-ventrally directed boss ; in the type-species there is only a stout ridge. The 



25mm 



foa 



par 



Fig. 87. Albula oweni (Owen). Neurocranium in right lateral view. 

 Based on B.M.N. H. P. 9158 and 39439. 



