ADJUSTMENT OF FLATFISHES 413 



mer flounder,' Paralichthys dentatus (MitchiU), and the 'winter 

 flounder' Pseudopleuronectes americanus (Walbaum), made it 

 evident that these, likewise, manifested interesting pigment 

 changes of an adaptive nature, but no systematic experiments were 

 performed. 



In the ensuing text, I shall first discuss the experiments with 

 Rhomboidichthys, and the less searching ones upon Rhombus, 

 at Naples; later the experiments upon Lophopsetta at Woods 

 Hole. 



2. EXPERIMENTS WITH RHOMBOIDICHTHYS PODAS." 



General description 



When first brought into the laboratory by the collectors, the 

 fishes were more commonly of a rather dark brown color, with in- 

 conspicuous darker and lighter markings (fig. 3c). This fact 

 makes it seem likely that they were generally taken upon the dark, 

 mixed sand, composed of finely divided lava and tufa, which is so 

 common in the Bay of Naples. On the other hand, some speci- 

 mens were fairly light when received, though never of a shade 

 even approaching the maximum degree of pallor which they at- 

 tained under experimental conditions. In a few instances, the 

 intra-annular areas (see below) were white or nearly so in the 

 freshly received specimen, giving to the latter a conspicuously 

 mottled appearance (fig. 7) . Such specimens, if we may judge from 

 the results of my experiments, had probably come from a bottom 

 diversified by white shell fragments. 



^' The collectors of the Stazione Zoologica recognize but one species of Rhom- 

 boidichthys, and Van Rynberk {op. cit.) refers to the species upon which he 

 worked as Rhomboidichthys {mancus seu podas). On the other hand, Canestrini 

 and others list two species, 'Rhombus podas' and 'Rhombus rhomboides,' which 

 are said to be very similar, differing chiefly in the distance between the eyes. 

 Moreau (Manuel d'Ichthyologie Francaise, '92, p. 469), under 'Bothus podas,' 

 cites Steindachner to the effect that there is but a single species of which 'B. 

 rhomboides' is the male and 'B. podas' the female. I have followed the usage of 

 the Naples Station in referring all my specimens to the same species, although 

 marked differences are to be noted in the shape, and especially in the distance 

 between the eyes. Compare, for example, specimens 3 and 4, plates 6 and 7. 



