OSTRACODElOl FISHES. 51 



the mouth is small and situated on the under side of the head. 

 The pectoral fins are large and set low down. The first dorsal fin 

 stands high and is almost continuous with the long second dorsal, 

 which itself is barely separated from the upper part of the tail fin. 

 There is a small anal fin separated by a short interval only from 

 the caudal. The caudal fin-membrane is about as high above as 

 below the axial part of the tail. Chimcera monstrosa, the Rabbit- 

 fish, 149, occurs in the Mediterranean and off the west coast of 

 Europe and Africa ; it is caught as far north as the Orkney Isles. 

 The American Elephant-fish or Spook-fish, Chimcera colliei, occurs 

 in the Pacific Ocean only and is found in less deep water than the 

 other Chimaeroids. Chimcera phantasma is a Japanese species. 



The Southern Elephant-fish, Callorhynchus antarcticus, 147, is Elephant- 

 distinguished by a remarkable cutaneous flap depending from the feh- 

 extremity of the rostrum. The tail is more distinctly heterocercal 

 than in Chimcera, and the second dorsal fin is more widely 

 separated from the first. A skeleton of Callorhynchus is shown 

 on the floor of the case (146). Harriotta, 157, is a fish which 

 grows to about two feet in length ; it has an elongated rostrum, 

 large pectoral fins, and the anal fin not separated from the caudal. 

 Harriotta occurs in about 1,000 fathoms in the West Atlantic, 

 and was first described in 1894. 



The Chimseroid fishes attained their greatest development, both 

 as regards number of genera and the size of the body, in the 

 Cretaceous and Eocene periods. Comparison of the tooth of 

 Edaphodon sedgwicki exhibited (155) with that of Callorhynchus 

 (148) and Chimcera (151) shows how much greater was Edaphodon 

 than the modern representatives of the Holocephali. 



OSTRACODERMI (Ostracoderm Fishes). 

 The Ostracodermi are extinct fishes, the remains of which occur 

 in Upper Silurian and Devonian strata. The head region is large 

 and broad ; calcified scales occur on the tail, and protective shields 

 on the front part of the body. Grooves on the surface of the 

 plates and shields indicate a well-developed system of dermal 

 sense-organs (lateral-line organs). The notochord was persistent, 

 and there were no differentiated vertebrae. Definite jaws seem to 

 have been wanting, and on account of this feature the Ostraco- 

 dermi are by some authorities associated with the Cyclostomi 



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