Plagiostomi — Sharks and Rays, 



13 



curious Chimaeroid affinities : upon the long snout of the male is 

 placed a slender prehensile spine (Fig. 11/), evidently homologous 

 with that of male Chimseroids. 



The Petal od on t idee comprise Carboniferous and Permian genera, Table-cases, 

 of which little is known beyond the dentition. Petalodus, Ctcno- Nos - 30 ' 31 - 

 ptychius, Petalorhynchu8j and Polyrhi%odun are Carboniferous forms : 

 and Janassa (Fig. 27), of which the dentition is very completely 



Fig. 27.— Some of the central teeth of Janassa linguceformis, posterior aspect, Coal-measures. 



understood, is both Carboniferous and Permian. These fishes were 

 evidently Rays. 



The Psammodontidcs are a group of Plagiostomes known only by 

 the detached teeth named Psammodus, so characteristic of the Lower 

 Carboniferous. They were evidently fishes of depressed form, refer- 

 able to the Rays ; and the Copodontidce, of this horizon, were also 

 probably similar. 



The well-known teeth of Ptt/chodus, from the Chalk, belong to 

 an uncertain family, but the specimens in the case show that the 

 genus must have been a huge form of Ray.* 



Various Pays of a modern type have been discovered in the Upper 

 Jurassic, Cretaceous, and Tertiary formations. The Rhinobatidce 

 are represented by Spathobatis, from the Lithographic Stone of 

 Bavaria, and Rhinobatus, from the Cretaceous of Mount Lebanon. 

 Of the Pr/stidce, or " Saw-fishes," fragments of the toothed snout are 

 shown from the English Eocenes. The " Sting-rays" (Tnjgonidre) 

 have an extinct representative, Cyclobatis, in the Chalk of Mount 

 Lebanon. The Raj/dce, or Skates and Pays proper, have left their 

 spinous dermal tubercles (Fig. 29) in the Pliocene Crags ; and the 

 great "Devil-fishes," "Sea-devils," and "Eagle-rays" (JI>/Iio- 

 batidce) are represented by numerous examples of their dentition, 

 especially of Myliobatis and Aetobatis, from the Tertiaries. 



The spines known as Myriacanthus, from the Lias, are also referred 

 to an unknown family of Pays. 



The Pleuracanthidce are a most remarkable extinct family charac- 

 teristic of the Carboniferous and Permian. As shown by nearly 



* Some of the modern Rays are said to attain an enormous size, and to weigh 

 many hundred pounds. 



Tble-case, 

 No. 31. 



Table-case, 

 No. 32. 



Wall-case, 

 No. 3. 



Table-case, 

 No. 33. 



Table-case, 

 No. 32. 



Wall-case, 

 No. 3. 



Wall-case, 

 No. 3. 



