8 ME. G. A. BOULENGEE ON A NOTHOSAUEIAN EEPTILE 



Assuming the specimen described in this paper to be the young of the larger Lario- 

 saurus balsami, the genus Lariosaurus is to be distinguished from Neusticosaurus by 

 the larger and more elongate skull, the shorter and broader radius, the shape of the 

 humerus, and the absence of notch in the pubis ; from Pachypleura and Dactylosaums 

 in the greater number of cervical vertebrae, the shorter and broader radius, and the 

 shape of the humerus ; and from the latter more particularly in the relative proportions 

 of the third and fourth fingers and the number of phalanges in the third finger. These 

 four genera may be conveniently grouped, for the present, under one family, Lario- 

 sauridaj, in many respects intermediate between the Mesosauridse and the Notho- 

 sauridse, although nearer the latter, as shown in the following attempt at a classification 

 of the Order Plesiosauria : — 



Order PLESIOSAUKIA. 



Skull with a single temporal arch. Dentition thecodont. Plastron present, not connected with 

 the clavicles. No ossified prsecoracoid. Sternum absent. Dorsal ribs single-headed. 



Divided into three Suborders. 



Before passing on to the diagnosis of the minor groups, I must observe that I reckon the so- 

 called " pectoral " vertebrae as cervicals, and that I accept Seeley's interpretation of the shoulder- 

 girdle. There is no evidence to show that the bar termed " precoracoid " in Chelonians constitutes 

 an element distinct from the scapula; therefore, I revert to the nomenclature o£ Cuvier and 

 Rathke, and term this bar acromial process of the scapula in both Chelonians and Plesiosaurians. 



I. Mesosauria. 



Clavicles present; scapulae fused with coracoids, the axes of which are transverse. Humerus 

 with entepicondylar foramen ; propodial bones elongate ; digits with not more than 5 phalanges. 

 Vertebra conically cupped, with persistent notochordal canal, without transverse processes; 

 cervical vertebrae 10 or 11 ; sacral vertebrae 4. 



A single family : — 



1. Mesosatjrid^:. 



II. NOTHOSAURIA. 

 Clavicles strongly developed, forming a bar across the pectoral region, embracing a small inter- 

 clavicle; scapulas with rudimentary acromial process; coracoids elongate, forming an angle, in 

 contact by their extremities. Humerus with entepicondylar foramen; propodial bones elongate; 

 digits with not more than 5 phalanges. Vertebrae biplane or feebly biconcave ; transverse processes 

 short or absent ; cervical vertebrae 16 to 21 ; sacral vertebrae 3 to 5 \ 



1. Lariosauridje. — Palate with infraorbital foramen. Dorsal vertebrae without transverse 

 processes. 



2. NoTHOsAURiDiE. — Palate without infraorbital foramen. Dorsal vertebrae with transverse 

 processes. 



1 Their number is still unknown in the 'Nothosauridse. However, Anarosaurus, Dames, which I would refer 

 to this family, is stated to have three sacrals. 



