Classijication of Teleostean Fishes. 303 



A distinct spinous dorsal fin ; anal spines detached 



from the soft portion ; a ventral spine ; gills 



three and a half, three slits between them. ... 1. Zeidae. 

 Dorsal and anal spines few, continuous with the 



soft rays ; a veutral spine 2. Amphistiidsei 



No spines ; cranium twisted in front, with the two 



orbits on one side ; gills four, a slit behind the 



fourth 3. Pleuronectidafe. 



According to our present information the three families 

 can be traced back to the Upper Eocene. The common 

 ancestors of the Zeidee and Amphistiidai will probably be 

 found in the Upper Cretaceous associated with the Berycidsej 

 to which they will no doubt prove to be related *. 



It is fair that I should add that the idea of deriving the 

 Pleuronectids from some form similar to Zeus had occurred 

 to Mr. E. W. L. Holt some years ago. He had been so 

 struck by the asymmetry in the number and arrangement of 

 the dorsal and anal bony plates in the young of the John 

 Dory that he induced his friend Mr. L. W. Byrne to examine 

 the matter on a large number of specimens between 2| and 5 

 inches in length, captured by Plymouth trawlers. This 

 study, which I hope Mr. Byrne may soon publish, demon- 

 strates the large proportion of specimens with an asymmetrical 

 arrangement of the plates and the apparent tendency to vary 

 esi)ecially in the direction of an asymmetry in which the 

 plates of the right or of the left side predominate. It is a 

 pity that so little should be known of the habits of the John 

 Dory, in view of the suggestion put forth a few years ago by 

 Verrill f, when dedilig with the sleep of some Labridje, first 

 observed by Mobius \. " The common Tautog or Black- 

 fish [Tautoga onitis),^^ says Verrill, " has the curious habit 

 of resting upon one side, half buried among gravel, or partly 

 under stones, and is often curved in strange positions. It is 

 easy to imagine that the flounders originated from some 

 symmetrical ancestral form that acquired, like the tautog, the 

 habit of resting upon one side, at first only when sleeping, 

 but afterwards continually, owing to the greater protection 

 that this habit and its imitative coloration afforded. The 

 one-sided coloration and the changes in the position of the 

 eyes, etc., would gradually follow in accordance witli well- 

 known laws of evolution." 



* On the ground of the number of ventral rays the Zeidae have been 

 brigaded with the Berycidse by Woodward (Cat. F.>ss. Fish. iv. p. 384), 

 t Amer. Jouru. Sci. (4) iii. 1897, p. 13tj. 

 X Zool. Garten, 1867, p. 148. 



