242 DR. A. T. MASTEEMAN ON A POSSIBLE CASE OF 



pectorals are perhaps better developed than in any other British flat-fish. 

 They are put to active use in swimming, but when a Dab is about to alight 

 on the sand, and its body is descending at an angle to the ground, it very 

 commonly holds the upper pectoral fin stiffly erect, possibly for the purpose 

 o£ guiding its descent. 



The Soles, as a family, have a characteristically elongated body. The 

 dorsal and anal fins are extended along its whole length'' and are specialized 

 as a means of locomotion. Probably in correlation with this feature the 

 family has a marked reduction in proportionate size of the pectoral fins as 

 compared with the Pleuronectidse, and the various subfamiles exhibit varying 

 stages of degeneration of these fins. They have been classified in accordance 

 with this feature. In the group of MonocMres there is only one pectoral fin,, 

 the right or upper. (^Solea monocliir of the Mediterranean.) 



In the Mic7'ochires, represented in British waters by the Thickback (Solea 

 variegata) and the Solenette (Solaa lutea), both pectoral fins are present, but 

 they are vestigial. They can be of little or no use for swimming purposes. 

 In the Solenette the right pectoral is often of a brownish tint, but I have 

 never seen it of the conspicuous black hue as shown in the figure by Couch. 

 In S. variegata the upper pectoral is inconspicuous and of the same tint as 

 the surface of the body. 



In the Sole {Solea vulgaris) and the Sand-Sole {Solea lascaris) the pectorals 

 are comparatively well developed. In the latter the black patch varies greatly, 

 from two or three black streaks or spots to a sharply-defined black blotch. 

 There appears to be some difference of opinion as to the black patch upon the 

 right pectoral of Solea lascaris. Couch is very decisive upon the point in 

 text and figures. Day figures and describes a black patch with a white 

 border. (Cunningham remarks in his text that the black patch is present, but 

 shows little trace of it in his excellent figure. An enquiry upon this point 

 indicates that whilst the black patch of the Sole is very conspicuous when the 

 fish is at rest, that of the Sand-Sole is largely if not entirely hidden by the 

 partial closing of the fin. In Cunningham's figure the fin is shown in the 

 closed condition and the black patch is scarcely recognizable. 



There are half-a-dozen Sand-Soles in the Plymouth Laboratory which have 

 resided in the tanks for two years or more. They show a right pectoral of 

 the same uniform tint as the rest of the body but with a few black streaks. 

 The coloration in this case may have undergone considerable change. Ac- 

 cording to Moreau, the pectoral is " jaunatre ou grisatre a la base et sur les 

 cotes, blanche a Pextremite ; elie est marquee dans sa partie moyenne et 

 posterieure d'une tache noire, arrondie, bien circonscrite '"' *. 



Similarly Dr. Griinther f describes the Channel Lemon Sole, under 



* ' Poissons de la France/ Part iii. pp. 309-310. 

 t Britisli Museum Catalogue, vol. iv. p. 467. 



