4 ICHTHYOPTERTGIA. 



arches attached by synchondrosis to flat surfaces on centrum. 

 Intercentra between the skull and atlas, and between atlas and 

 axis. Dorsal ribs double-headed. Hibs present in the caudal 

 region ; no uncinate processes ; chevrons not united inferiorly. 

 Abdominal ribs present ; no sternum. In pectoral girdle (fig. 4) 

 clavicles and a T-shaped interclavicle ; coracoids not overlapping, and 



Pig. 3. 



Ichthyosaurus (cf.) entheciodon. — The centrum of an anterior dorsal vertebra, 

 viewed in section, and from the anterior and left lateral aspects ; from the 

 Kiineridge Clay of Wiltshire. £. 



Pig. 4. 



Ichthyosaurus (cf.) communis. — Ventral aspect of the pectoral girdle. Reduced. 

 ic, interclavicle ; cl, clavicle ; cor, coracoid ; sc, scapula ; gl, glenoid 

 cavity. (From the 'Proc. Geol. Soc.') 



without fontanelle ; no distinct precoracoid. Pelyis weak ; ilia not 

 connected with vertebrae ; and an open obturator notch. Humerus 

 and femur much longer than radius and tibia ; no foramen in 

 humerus ; when one limb is longer than the other the superiority is 

 with the pectoral. 



