creatures are frequently subject to 

 confusion. Scientific names of Greek 

 or Latin derivation are frequently re- 

 duced to English form and used as 

 English common names. Chimaera is 

 such a name (derived from the Greek 

 chunair, meaning goat), and it is useful 

 because it covers all one closely re- 

 lated group of cartilaginous fishes in- 

 cluding some known as ratfishes, some 

 as elephant fishes, and others. Elasmo- 

 branch is another word (derived from 



the Greek words elasmo, nn e a n i n g 

 platelike or si it like, and branchia, 

 meaning gill) ■which has come into 

 common usage and which refers to any 

 shark, skate, or ray, but not to chi- 

 maeras. The anglicized ^ord selachian 

 (from the Greek term coined to desig- 

 nate fishes having cartilaginous skele- 

 tons instead of bone) has become even 

 more restrictive and now refers 

 only to sharks, not to skates or 

 rays. 



CLASS CHONDRICHTHYES, THE CARTILAGINOUS FISHES 



Members of the class Ghon- 

 drichthyes, the sharks, skates, rays, 

 and chimaeras, possess well-developed 

 lower jaws which set them apart from 

 the lampreys, hagfish, and other lower 

 vertebrates; and they possess skeletons 



which are composed of cartilage rather 

 than true bone, a feature which sets 

 them apart from the bony fishes and 

 other higher vertebrates. The car- 

 tilaginous skeletons, how^ever, are often 

 made up of structural components that 



AVES (Birds) 



MAMMALIA 



REPTILIA 



AMPHIBIA 



CHONDRICHlVfE's (Cartilaginous fishes) OSTEICHTHYES (Higher bony fishes) 



PLACODERMI (Archaic jawed fishes) 



AGNATHA (Jawless fishes) 



} 



NON-VERTEBRATE CHORDAnS 



'Family tree" of the vertebrates illustrating, m theopinionof many zoologists, 

 the relations existing among members nf the group. 



