204 MR. E. T. NEWTON ON SOME [-^P'"- 2, 



the indentations of the margin are alike in the two forms, hut the 

 supraoccipital of the fossil is evidently a shorter and wider bone, 

 and it is uncertain whether it was constricted in the middle or not. 

 The supraoccipital of A. e(jertoni is only slightly constricted, and 

 it may be that the Barton skull, here described, more resembled 

 that species. 



Several of the anterior vertebrfe of A. yaf/orides are united to 

 form one mass, in a manner precisely similar to that which obtains 

 in the fossil. 



The differences above noted show clearly that the recent and 

 fossil forms are specifically distinct, while at the same time the 

 resemblances are sufficiently important to prevent a generic separa- 

 tion ; but there is still some additional evidence which supports this 

 decision in an unexpected manner. 



While clearing away the matrix from the right side of the fossil 

 skull, where it is broken near the back, I was fortunate enough to 

 find one of the otoliths in place, and this, when extracted, proved to 

 he of a remarkable form (figs. 3, a, b, c), and quite unlike the otolith 

 of any fish with which I was acquainted. 



"When found, this otolith had the more pointed end directed back- 

 wards and outwards, with the smooth surface upwards ; and as it 

 seemed to be in its natural cavity, for the present this is regarded as 

 its proper position ; but seeing that the otolith of the opposite side 

 is not in its place, and that in the diied skull of the receut species 

 they are loose in the brain-cavity, this may not be correct. 



The otolith is proportionately large and thick, its upper surface 

 («) is smooth and convex, while its lower surface (6) is rugose and 

 much more convex. At firs,t sight there appears to be no sulcus 

 acHsticus, but probably it is represented by the sinuous groove on 

 the lower surface which passes from the hinder pointed end to the 

 opposite extremity, that is between the two stars in figure 3 b. The 

 rugosity of the under surface is due to a number of concentric 

 striations, or lines of growth, crossed by several radiating ridges 

 which are stronger on the inner than on the outer portion. One of 

 the radiating ridges is especially strong, and forms a prominent angle 

 where it reaches the inner niargin, towards the front of the otolith 

 (fiff. 3 b, x). The pointed extremity is seen to be notched, a slight 

 groove extending from this both on the upper and lower surfaces 

 (figs. 3 a, b). From this bifid point a shallow groove extends along 

 the outer margin, becoming a mere line towards the front ; it is seen 

 in an upper view (fig. 3 a), and is separated from the smooth upper 

 surface by a fine but distinct raised line. 



A similar otolith to this is figured by Herr E. Koken, from the 

 Oligocene of Headon Hill, Isle of Wight ((i), who, having no clue 

 to its aftinities, called it Otolithus (incertcB seclis) crassus. 



The close relationship between the recent Arins guyorides and the 

 Barton fossil skull made it particularly desirable to sec whether the 

 otoliths would show a corresponding resemblance, and Dr. Giinther 

 very kindly had the otoliths taken out of the skull with which the 

 above comparisons had been made. One of these otoliths is repre- 



