ACTINOPTERYGII. 97 



of Ntylitonn teeth, and bearing at its inner extremity a very large ascend- 

 ing process which fits into a groove on the inferior aspect of the frontal 

 bones. The large parasphenoid bears no teeth, but the two vomers are 

 fused together into a stout bone which is provided with crushing teeth. 

 The dentigerous bones of the palato-pterygoid arcade are closely connected 

 with the vomer in front and similarly thickened. The hyomandibular is 

 not pierced by any foramen, and the quadrate is remarkably delicate. 

 The rnetapterygoid is also comparatively delicate, but shows a broad 

 facette on an upwardly directed process, which may have articulated with 

 some lateral element of the cranium. The hinder portion of the meckelian 

 cartilage is ossified, and to its outer face there is apposed a large angular 

 plate, and the coronoid elevation is completed above by a small coronoid 

 (surangular) bone. The dentary bone, very deep in the coronoid region, 

 becomes much narrower in its tooth-bearing portion ; and a roughened 

 surface on its inner face articulates with the robust spleuial bone, which 



Fia. 69. 



Lepidotus minor ; restoration, about one-fifth nat. size. U. Jurassic (Purbeck 

 Beds) ; Dorsetshire. (From Brit. Mus. Catal.) 



also enters the symphysis. Whereas the dentary bears only one series of 

 teeth, the spleuial has several irregular series of a more tritoral character. 

 All the teeth are hollow, and when viewed in section, the calcigerous tubes 

 in the dentine are shown to radiate from the central cavity. Successional 

 teeth are numerous, and each germ turns through an angle of 180 as it 

 gradually comes into use. The opercular apparatus is complete and 

 there is a good series of branchiostegal rays ; but no gular plate occurs. 

 The branchial arches are delicate, and there are calcified supports for 

 the gill-filaments, while small pointed gill-rakers are arranged in a 

 sparse series. The notochord is proved to have been persistent, and 

 in the earlier and smaller species no ossifications have been observed 

 in its sheath ; but in the large Wealden, and perhaps also in the large 

 Oxfordian species, there are distinct indications of ring- vertebrae at 

 least in the abdominal region. The ribs are ossified, and borne on 

 short processes of the hypocentra when these ossifications occur. The 

 right and left halves of the neural arches in the abdominal region are 



w. 7 



