The Holocephali, or Chimaeras 



565 



and the huge jet-black Chimara purpurascens in Hawaii and 

 Japan. None of these species are valued as food, but all impress 

 the spectator with their curious forms. 



The fossil Chim&ridce, although numerous from Triassic 

 times and referred to several genera, are known chiefly by their 

 teeth with occasional fin-spines, frontal holders, or impressions 

 of parts of the skeleton. The earliest of chimaeroid remains has 



FIG. 352. Elephant-fish, Chimcera colliei Lay & Bennett. Monterey. 



been described by Dr. Charles D. Walcott* from Ordovician 

 or Lower Silurian rocks at Canon City, Colorado. Of the species 

 called Dictyorhabdus priscus, only parts supposed to be the 

 sheath of the notochord have been preserved. Dr. Dean thinks 

 this more likely to be part of the axis of a cephalopod shell. 

 The definitely known ChimcsridcB are mainly confined to the 

 rocks of the Mesozoic and subsequent eras. Ischyodus priscus 

 (avitus) of the lower Jura resembles a modern chimaera. 

 Granodus oweni is another extinct chimaera, and numerous 

 fin-spines, teeth, and other fragments in the Cretaceous and 

 Eocene of America and Europe are referred to Edaphodon. A 

 species of Chim&ra has been recorded from the Pliocene of 

 Tuscany, and one of Callorhynchus from the greensand of New 

 Zealand. Other American Cretaceous genera of chimaeroids are 

 Mylognathus, Bryactinus, Isotania, Leptomylus. and Sphagepcea. 

 Dental plates called Rhynchodus are found in the Devonian. 



Rhinochimseridse. The most degenerate of existing chimaeras 

 belong to the family of Rhinochimaridce , characterized by the 

 long flat soft blade in which the snout terminates. This struc- 



* Bulletin Geol. Soc. America, 1892. 



