No. 439-] 



NOTES AND LITERATURE. 



left nerve is uppermost in 24, the right nerve in 25. Among sinistra] 

 soles, or tongue fishes, in iS individuals of two species, the left nerve 

 is uppermost in 13, the right nerve in 5. 



Professor Parker concludes from this evidence that soles are not 

 degenerate flounders, but rather descended from primitive flounders 

 which still retain the demorphic condition as to the position of the 



The lack of symmetry among the flounders lies therefore deeper 

 than the matter of the migration of the eye. The asymmetry of the 

 mouth is an independent trait, but like the migration of the eye. is 

 an adaptation to swimming on the side. Each of the various traits of 

 asymmetry may appear independently of the others. 



The development of the monomorphic arrangement in flounders, 

 Professor Parker thinks, can be accounted for by the principle of nat- 



has a mechanical advantage. The unmetamorphosed young of the 

 flounder are not strictly symmetrical, for they possess the monomor- 

 phic position of the optic nerve. The reversed examples of various 

 species of flounders (these, by the way, chiefly confined to the Cali- 

 fornia fauna) afford "striking examples of discontinuous variation." 



Professor Parker inclines to the opinion that the ancestral floun- 

 ders were allied to the john dories. This is as plausible a guess as 

 any. They certainly have no affinity with the cod-fishes. 



Notes on Recent Fish Literature.— Mr. C. T. Regan {Proc. ZobL 

 Soc. London) takes up the osteology of the plectognathous fishes 

 and the classification derived from it. The chief character of the 

 group as distinguishing it from their ancestors, the Acanthuridx is 

 the absence of ribs. He divides the plectognaths into two divisions, 

 the Sclerodermi and the gymnodontes. To the former group the 

 Ostracodermi are referred. The supposed families of Chonerhinida- 

 and Tropedechebyidje are regarded as not distinct from Tetraodon- 

 tida; and doubt is thrown on the accuracy of the figures of Hollard 

 which have served as the basis for certain generic distinctions. 



The Mexican trigger-fish Batistes naufrctgium is said to be a spe- 

 cies of Xanthichthys, a genus rejected by Mr. Regan. 



