Plagiostomi — Sharks and Rays. 



5 



From the perishable nature of their skeletal parts, it is obvious 

 that the palaeontological history of these fishes is most difficult to 

 decipher. In the majority of instances, the fossils consist merely 

 of detached spines, shagreen-granules, teeth, or pieces of cartilage; 

 and it is often impossible to correlate these unsatisfactory frag- 

 ments, so that the different parts of the same species not unfre- 



Fig. 10. — The Ray {Raja Murrayi, Giinther), from Kergrulen's Island. 

 A, dorsal aspect ; B, part of ventral side ; sp, spiracle ; br, branchial clefts ; m, mouth. 



1 1 



'.'•ft 



,3 



Fig. 11. — Spines of Plagiostomous and Chimaeroid Fishes. 

 a, Acanthias (recent); b, Callorhyiichus (recent); c, Machceracanthus (Devonian); 

 d, JTybodu.s (Jurassic); e, Aster acanthus (Jurassic): /, Squaloraja (Lias); 

 a, Gyr acanthus (Carboniferous); A, Edestes (Carboniferous); i, Pleuracanthus 

 (Carboniferous). 



quently receive even distinct generic names. Sometimes, however, Wall-case, 

 complete fishes are met with, and many beautiful examples are No - 3 - 

 shown from the Lias of Lyme Regis, the Lithographic Stone of 

 Bavaria, and the L^pper Cretaceous of Mount Lebanon. 



