14 ICHTHYOPTERYGIA. 



In the Cretaceous and Kimeridgian species the entire paddle is 

 unknown, and its structure can only be inferred from the corre- 

 spondence of its radius with that of the Liassic forms, and of the 

 humerus with that of Ophthalmosaurus. If it should be found that 

 any of the species differ in the arrangement of the digits of the 

 paddle from the typical subgroup, the structure of the radius will 

 have to be made the primary distinctive character of the Lati- and 

 Longipinnate groups. 



a. Campylodont Subgroup. 



The roots of the teeth (fig. 11) enveloped in a thick layer of 

 cement, which generally assumes a more or less bulbous form, and 

 may be angulated. Coracoid (when known) without posterior notch ; 

 scapula (when known) with prominent ridge on anterior border of 

 dorsal surface of proximal extremity. Humerus (fig. 9) and femur 



Fig. 9. 



Ichthyosaurus (cf.) trigonus. — Dorsal and distal aspects of the right humerus ; 

 from the Kimeridge Clay of the Isle of Portland. ^. a, trochanteric 

 ridge ; r, radial, u, ulnar facet. 



with strongly developed trochanteric ridges. Cervical and ante- 

 rior dorsal vertebrae with pentagonal, subcordiform centra (fig. 7) ; 

 and the superior costal articulation of the former in great part or 

 entirely on the neural arch (fig. 7) ; late posterior dorsal and an- 

 terior caudal centra narrowed superiorly. 



