OECELLA. 



The dimensions of these bones are — 



365 



Length of periotic t* 



„ „ tympanic through anterior lobe ........ 



„ „ „ ,, posterior „ ........ 



Breadth of tympanic at middle ... ...... 



Greatest breadth , . 



0. brevirostris. 



1-56 

 156 

 1-44 



0-88 

 1-00 



Table of measurements of the skulls of Orcella brevirostris and Orcella fluminalis. 



Extreme length of skull in a straight line 



Greatest breadth across squamosals 



Length of snout from transverse line on preorbital notch 



Breadth of snout at preorbital notch ...... 



„ midway between preorbital notch and tip of snout 



„ between same points, following curve .... 



Width of snout immediately behind its tip ..... 



Breadth of occipitals between parietal sutures measured with calipers 



Greatest breadth across condyloid articular processes 



Distance between condyles at lower margin of foramen magnum 

 „ „ occipital condyles at upper ditto .... 



Greatest breadth of each occipital condyle 



„ length of same along curve 



Length of foramen magnum 



Breadth of „ „ 



Width between lateral expansions of basisphenoid .... 



Greatest length of pterygoids on palatal surface . . . . 

 „ „ of palatines in middle line of palate 

 „ width of narial aperture 



0. brevirostris. 



10-32 



1100 



11-72 



11-32 



6-68 



7-00 



8-0O 



7-64 



4' 54 



4-64 



5-24 



4-64 



3-56 



4-08 



4-32 



4-08 



1'56 



1-32 



1-56 



1-56 



2-72 



2-64 



3-00 



2-80 



072 



0-64 



0-72 



1-00 



4-64 



5-56 



5-56 



5-56 



2-48 



2-80 



3-08 



3-48 



0-72 



0-80 



0-88 



0-72 



1-24 



1-48 



1-40 



1-40 



0-88 



1-04 



1-40 



1-48 



2-48 



2-48 



3-00 



3-00 



1-56 



1-72 



1-48 



1-80 



1-16 



1-32 



1-32 



1-80 



2-72 



3-00 



3-48 



3-16 





1-64 



1-86 



1-80 



0-20 



0-16 





0-56 



1-73 



1-72 



1-88 



1-80 



O. fluminalis. 



12-16 

 8-16 

 5-00 

 4-64 

 2-00 

 3-32 

 1-16 

 5-72 

 3-16 

 0-88 

 1-48 

 1-32 

 2-72 

 1-72 

 1-72 

 3-64 

 2-00 

 0-64 

 1-84 



Dentition. — The visible teeth are i; H J; H, but in the upper maxillary, after 

 the flesh was removed, two on the right, and three additional sockets on the left 

 side, were displayed. The anterior teeth are much larger than those behind them, 

 and each is separated from its fellow by a very thin rough septum. In the left 

 division of the lower jaw the sockets are larger and deeper than in the upper jaw, 

 and on the right side fourteen sockets are well marked. Moreover, in the rough 

 surface that succeeds the last tooth upon each side of the lower jaw, there are indi- 

 cations of what may have been the sockets of two other teeth. The first tooth in 

 the upper jaw is fully 0"*28 from the extremity of the premaxillaries, which are par- 

 tially worn, as if they had been undergoing decay. In the adolescent skull these 

 bones are almost intact at their tips. Prom the circumstance that the adult skull of 

 0. brevirostris in the fresh state only contained eight teeth in the upper jaw, 

 whilst when the jaws were freed of flesh they displayed a number of empty sockets 

 on both sides, it is evident that that form, and in all probability its near ally, O. flu- 

 minalis, lose their teeth with age from behind forwards ; likewise, that in the fully 

 matured condition they only retain eight or nine of the anterior teeth on each side 

 above and below. Decay seems to begin in the centre of the tooth, which is gra- 

 dually destroyed, leaving only the hard shell, which continues to project for some 



