226 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



We recognize amoug the Plcuroncctidw seven subfamilies — Hippo* 

 glossince, Pleuronectince, Samarinw, Platessinw, Oncopterinw, Soleinw, and 

 Cynoglossince. The Samarincc and Oncopterinw are all of recent disco-v- 

 ery. The other groups correspond exactly to the five u subgenera" 

 {Eippoglossus, Rhombus, Platessa, Solea, and Plagusia) recognized by 

 Cuvier. These subfamilies are natural groups and are in most cases 

 easily distinguished, although some few aberrant genera exist which 

 serve as links joining one group to another. Thus Isopsetta of the 

 Platessinw is certainly a near ally of Psettichthys, which is as certainly 

 a genuine member of the Hippoglossina : 



The Hippoglossinw and the Platessinw are largely arctic in their dis- 

 tribution, few of the former group and none of the latter extending into 

 the tropics. The Oncopterince seem to take the place of the Plates- 

 sinw in antarctic waters, but the species of this group are few in num- 

 ber. The Pleuronectince and the soles are, on the other hand, essentially 

 warm-water fishes, their representatives in the north being compara- 

 tively few. The Samarinw are few in number and belong to the East 

 Indian fauna. 



As the tropical Hippoglossinw and all the Pleuronectinw are sinis- 

 tral species, the eyes and color being on the left side of the body, it fol- 

 lows that the tropical flounders are nearly all left-sided species, while 

 those of arctic and antarctic waters are chiefly dextral species, the 

 eyes and color on the right. 



Still more curious is the relation between the number of vertebra 

 and the geographical distribution of the various species. 



It has been already noticed by Dr. Gunther and others that in some 

 groups of fishes northern representatives have the number of vertebras 

 increased. In no group is this more strikiug than in the flounders, as 

 the following table showing the numbers of the vertebras in various 

 species will clearly show. The numbers inclosed in brackets are copied 

 from Dr. Gunther ; the others represent our own count of specimens con- 

 tained in the museum of the Indiana University. 



Numbers of vertebras in flounders. 



I. — Hippoglossin.e. 



Hippoglossus hippoglossus 16 -f- 34 = 50 



Atheresthes stomias 12 -f- 37 = 49 



Hippoglossoides platessoides 13 -j-32 = 45 



Lyopsetta exilis 11 -f- 34 = 45 



Eopsetta jordaui ll-|-32= 43 



Psettichthys melanostictus 1 1 -f- 29 = 40 



Paralichthys oblongHs 11 -(-30= 41 



Paralichthys dentatus 10 -f- 30 = 40 



Paralichthys lethostigma 10 + 27= 37 



Paralichthys albigutta 10 -f- 27 = 37 



Paralichthys californicus 10 + 25 = 35 



Xystreurys liolepis 12 + 25 = 37 



Ancylopsetta quadrocellata . - - !» -f- 26 = 35 



