CLASSIFICATION 35 



the European B. podas the adults of the two sexes are so unUke that they were originally 

 described as distinct species (Fig. 22).^ Even in young males, however, the inter- 

 orbital space is already broader than in females of the same size, although the 

 characteristic spines, protuberances and roughened ridges on the head do not make 

 their appearance until later. 



The form of the fins, and more particularly of the dorsal fin, may present sexual 

 differences in certain species. In some, for example, the anterior dorsal rays in the male 

 are prolonged to a greater extent than the corresponding rays in the female (e.g. 

 Arnoglossus imperialis (Fig. 23), Lophonectes galliis, Marleyella bicolorata) ; in others, 

 these rays may be very elongate in the male and of normal length in the female {e.g. 

 Arnoglossus iapemosoma, Brachyphura novel zeelandieE). In other genera (e.g. Samaris) 

 this elongation of the anterior dorsal rays may occur in both sexes. In the genus 

 Tesniopsetta, instead of the anterior rays, it is the loth to 13th as far as the 13th to 

 i8th rays of the dorsal fin that are prolonged. In Arnoglossus, Marleyella, and one 

 or two other genera, some or all the rays of the pelvic fin, or at least of that of the 

 ocular side, are more or less elongate in the male, and in Trrniopsetta the first few rays 

 of the anal fin are prolonged. 



It is of interest to note that in such genera as Bothus and Arnoglossus the species 

 present considerable variation in the degree to which the sexes are difierentiated. In 

 Arnoglossus imperialis, for example, the first few dorsal rays are very much more 

 elongate in the male than in the female, whereas, in the closely related A . laterna and 

 A . thori, apart from a very slight difference in the pigmentation (the black spot on 

 the pelvic fin of the ocular side is darker in the male), the sexes are alike. ^ 



Finally, Marleyella bicolorata exhibits a form of sexual dimorphism unknown in 

 any other Flatfish. The anterior rays of the dorsal fin, as well as those of the pelvic 

 of the ocular side, are much longer in the male, and, in addition, the teeth on the ocular 

 side of the upper jaw extend on to the outer surface of the jaw in this sex. 



VII. CLASSIFICATION. 

 A. GENERAL. 



The earher ichthyologists nearly all regarded the Flatfishes as constituting a single 

 family, Pleuronectidee. This was the arrangement adopted by Jordan and Goss 

 (1889, p. 225), who further subdivided the family into seven subfamilies : Hippo- 

 glossinae, Pleuronectins,^ Samarina;, Platessius, Oncopterinae, Soleinae and Cyno- 

 glossinae. Leaving out the Samarina; and Oncopterinae, the members of which were 

 unknown in his time, the remaining five subfamilies defined by Jordan and Goss 

 correspond respectively to the genera Hippoglossus, Rhombus, Platessa, Solea and 

 Plagusia of Curvier (1817). Jordan and Goss recognised the distinctness of the 

 " Soles " from the " Flounders ", but stated that " the characters which mark them 

 as a group seem no more important than those which set off one subfamily of flounders 

 from another." These authors also showed that the Bibroniidae, a family of Flat- 

 fishes recognised by some Italian ichthyologists, is composed entirely of larval forms 

 and has no place in the system. Jordan and Evermann (1898, p. 2602) included the 

 Flatfishes in a single suborder, Heterosomata, and recognised two distinct famiUes, 

 Pleuronectidae and Soleidae, the last including the Tongue Soles (Cynoglossus, 

 Symphurus) as well as the true Soles. The Pleuronectidae were further subdivided by 

 them into Hippoglossinae, Pleuronectinae and Psettinae, and the Soleidae into Soleinae 

 and Cynoglossinae. 



^ The associated chaages in the cranium of old males have been described by Kyle (1921, 

 p. 78, figs.). 



' See Kyle (1913. PP- 30, 94)- 



^ Rhombinse, Psettins or Bothin* of other authors . . . Scophthalmins in this work. 



