THE GANOIDEI. 139 



scales, wliich not only overlap, but are fitted together by- 

 pegs and sockets, where their anterior and posterior edges 

 come into contact. 



The endoskeleton is not less diversely modified ; and it is 

 worthy of remark that no sort of relation, either direct or 

 inverse, is traceable between the completeness of the endo- 

 skeleton and that of the exoskeleton. Thus Spatularia, 

 Scapirhynchus, and Accipenser have a persistent notochord, 

 in the sheath of which mere cartilaginous rudiments of the 

 arches of vertebrae appear. The ribs, when present, are 

 partially ossified. Polypterus and Amia have fully ossified 

 vertebrae, the centra of which are amphiccelous. Lepidosteus 

 also has fully ossified vertebrse ; but their centra are opis- 

 thoccBlous, having a convexity in front and a concavity 

 behind, as in some Amphibia. 



More or fewer of the anterior vertebrse, or their cartila- 

 ginous representatives, are united with one another, and 

 with the posteiT.or part of the skull. And the cranium may 

 consist principally of cartilage, membrane bones being super- 

 added ; or the primordial cartilage may be largely super- 

 seded by bone, as in the Teleostei. 



Spatularia, Scapirhynchus, and Accipenser- have skulls of 

 the former description. The cranium is one mass of car- 

 tilage, continiious behind with the coalesced anterior spinal 

 cartilages, so as to be immoveably connected with the spinal 

 column. The notochord enters its base, and terminates in 

 a point behind the pitiiitary fossa. In front, the cartilage 

 is produced into a beak, which, in Spatularia, is very long, 

 flattened, and spatulate. In the perichondium of the base 

 of the skull, median bones, answering to the vomer and to 

 the parasphenoid of Teleostean fishes, are developed ; and, 

 in that of its roof, ossifications, which represent the parie- 

 tals, frontals, and other membrane bones of the Teleostei, 

 appear. 



The framework of the jaws in Spatularia is very similar 

 to that in the Elasmobrancliii, There is a partly carti- 

 laginous, and partly ossified, suspensorial cartilage (A, B, 

 Fig. 39), which gives attachment below, directly, to the 



