The Embryology of Heterodontus japonicus 



695 



Text-figure 27- 



Hyhodus hauffianus E. Fraas : skeleton, with skin (shagreen) outlining the entire body which is about 



2240 mm. (88 inches) long. Upper Lias; Holzmaden, Wiirttemberg. 



After Koken, 1907, Taf. I. 



applied to present-day representatives of the group. Of greater importance is the close 

 relationship between the Heterodontidae and the Hybodontidae, which will now be 

 discussed. Since paleontologists almost uniformly use the term Cestracion instead of 

 Heterodontus, and Cestraciontidae in place of Heterodontidae, it is advisable, in review- 

 ing their work, to adopt their language without a tiresome repetition of synonyms. . 



In his "Catalogue of the Fossil Fishes in the British Museum", Woodward (1889) 

 defined the Cestraciontidae very broadly as follows : ''Dorsal fins each armed with a spine, 

 the first opposite to the space between the pectoral and pelvic fins. Teeth mostly obtuse, 

 never fused into continuous plates; several series simultaneously in function". He 

 further states that "No distinctive characteristics of value having yet been discovered, 

 the so-called Orodontidae and Hybodontidae are included in this family". 



This classification, or something like it, seems to have been adopted by Goodrich 

 (1909) since he includes Orodus and Hybodus (the latter portrayed in my Text-figures 27 

 and 28) in the family Cestraciontidae. Regan (1906) had already separated the Ces- 

 traciontidae from the Hybodontidae. Most of the characters that Regan lists for the 

 two families are identical, but he states that in the Cestraciontidae the pterygoquadrate 



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Text-figure 28. 



Reconstruction of the skeleton and outline of the body of Hyhodus hau^anus E. Fraas, based on a 



specimen about 1220 mm. (48 inches) long. Upper Lias of Hohmaden, Wiirttemberg. 



After Jaekel, 1906, Fig. 2. 



