KINSHIPS OF SHARKS 



97 



survived among the widely evolved genera and families of 

 Palaeozoic times. 



5. The more primitive types of modern sharks, Chlamy- 

 doselache, Notidanus, represent in an almost differentiated 

 condition the Palaeozoic phylum. 



6. The modern rays are derived in early Mesozoic times 

 from the main shark stem, not (in the opinion of the 

 writer) descended from Cestracionts, Pristids, Pristiopho- 

 rids, or even (?) Rhinids. 



7. Chimaeroids, next to be discussed, represent the most 

 ancient of known offshoots from the (Pre-Silurian ?) sharks : 

 they are not degenerate in their essential structures, nor 

 are they connected with the ancestral phylum of the lung- 

 fishes, save through a common descent from early shark- 

 like ancestors. 



These results the writer has expressed in the diagram 

 on the following page. The diverging phyla are indicated 

 as they are represented historically ; their primitive con- 

 currence with the main line of descent is suggested by 

 dotted lines. 



