HO LOST El 



327 



occipital is derived from neither of these sources, but is a new 

 ossification. 



The intestinal spiral valve is already much reduced in Amia and 

 Lepidosteus ; in the Teleostei it usually disappears altogether. 



Via. 305. 



Salnto solar, L. (After Uruch.) A, skull from behind. B, transverse section of the trunk. 

 C, transverse section of a trunk vertebra, bo, basioccipital ; bi\ basiventral ; c, centrum ; ep, 

 Kpipk-iiral ; epo, epiotic ; exo, exoccipital ; f.m, foramen magnum ; li, longitudinal ligament ; my, 

 myotome ; n.e, neural canal ; n.s, neural spine ; op, opisthotic ; pa, parasphenoid below the 

 myotlome ; p.r, pleural rib ; pto, pterotic ; r, rib ; so, supraoccipital. 



Order 1. AMIOIDEI. 



The three sub-orders of the Holostei differ in the structure of 

 the vertebral column. In the Amioidei the notochord is sharply 

 constricted by well-formed centra in the only living species, Amia, 

 calca, but in the earlier, more primitive forms it appears to have 

 persisted to a much greater extent. The Amioidei are distinguished 

 by the presence of separate pleuro- and hypocentra, at all events 

 in a certain region. In the Actinopterygii we have hitherto 



