Evolution of the < h-dn- llitei'osomata. 4^7 



below ; tlio pelvic fin, ])ro»(»rvcd only in tlio ^foiite BoIc;i 

 speciuKMi, \A fonued of a spine and, in my opinion, 5 soft rays, 

 for I cannot see a greater number inserted on the pelvic l)one 

 wliicli lies up|)ermo8t, tlie outlines of wliicli are fairly distinct. 



Boulfn;^i'r's restoration shows several features of P.seltodi's 

 or Xetts rather than J'scttus which I am unable to see in the 

 iossils ; thus he shows the lower jaw nearly as lon;^ as the 

 head and the pra.'operculiim vertical and scarcely curved, 

 whereas tlie lower jaw appears to me only a little more than 

 linlt the length of the head, and the prieoperculum to have a 

 distinct lower limb ; also the origin of the anal fin is not so 

 far forward in th-' actual fossils as it is in the restoration. 



Jiothua and Sulni were already in existence in the Upper 

 Kocene, and, indeed, the whole Upper Eocene fish-fauna is 

 strikingly modern, so that there is no reason to regard 

 Anif/iistiuin as ancestral to the flat-fishes on account of its 

 occurrence in the Upper p]ocene. 



The researches of Parker * on the optic chiasma are of 

 great importance for the classification of the Ileterosomata. 

 He found that in various symmetrical Teleosts the left nerve 

 crossed above the right about as frequently as the right above 

 the left; this was also the case in flat-fishes of the family 

 k^oleida; as recoguized by Jordan and Evermann f, whether 

 dextral {Sotea, Achirua) or sinistral {Si/mphnrus). From 

 this dimorphism of the chiasma it follows that in the Soleidae 

 the optic nerves are partly uncrossed when the nerve of the 

 migrating eye is dorsal, and that they almost cross each other 

 twice when it is ventral. In other flat-fishes, whether dextral 

 (^Paettichthys^ Atherest/ies, Parophrys, Pleuronectes, &c.) or 

 sinistral {Paralichthys, Platojthrys, Cithan'chthys^Sic.) ^ Parker 

 fuund tiiat it was always the case tiiat the nerve of the 

 migrating eye was dorsal, the only exception being in the 

 case of reversed examples, /. e. sinistral members of dextral 

 species or dextral members of sinistral species, in which that 

 nerve was dorsal which was normally dorsal in the genus. 

 In a few species of the Pacific coast of North America sinistral 

 and dextral individuals are equally numerous ; but in a species 

 of a sinistral genus, such as Panilic/ithys cuHfornicus, the 

 nerve of tiie right eye is always dorsal, wliether the individual 

 be sinistral or dextral; similarly, in a species of a dextral 

 genas, such as Platichthya siellatus^ the nerve of the left eye 

 is dorsal. This monomorphism of the optic chiasma is 

 obviously a specialization, wliich Parker considers has beeix 



• Bull. MuB. Comp. Zool. xl. pp. 219-242 (19a3). 



t IJull. U.S. Nat. Mu8. xlvii. pt. iii. pp. 2602-2712 (1898K 



