280 "ENDEAVOUR" SCIENTIFIC RESULTS. 



Apsetta thompsoni, Kyle, 11 differs from all the known 

 species of Rhombosolea in having the eyes on the left 

 side, and in the presence of two equally developed pelvic 

 fins. In all other characters it appears to be identical 

 with 7?. plebeia, and probably represents a reversed 

 example of that species; according to Hutton (Trans. 

 N.Z. Inst, VIII, 1876, p. 215) such examples are not 

 uncommon. In the specimen of Apsetta the reversal 

 appears to have been accompanied by the development of 

 two equal pelvics, but there may have been some degree 

 of ambicoloration, for Hutton (iUd, VI, 1874, p. 106, pi. 

 XIX) has described a reversed example with a single 

 pelvic fin joined to the anal as in normal specimens of 

 Rhombosolea. 



Among the specimens of R. tapirina in the collection 

 of the British Museum (Nat. Hist.) is a reversed example 

 from Dunedin. In this specimen the left pelvic is median 

 and is joined to the anal as in Apsetta ; the right pelvic 

 is also present but is lateral, short-based, and is com- 

 posed of only 4 rays, the first of which is inserted 

 opposite the space between the fifth and sixth rays of the 

 left pelvic. 



The researches of Parker 12 on the optic chiasma of 

 Flatfishes have shown that in the suborder Pleuronec- 

 toidea the nerve of the migrating eye (i.e. the left eye 

 in Rhombosolea) is always dorsal to that of the other 

 eye, except hi reversed examples, in which that nerve is 

 dorsal which is normally dorsal in the genus. Thus, as 

 far as the optic nerves are concerned, a reversed example 

 is not an exact mirror-image of a normal one, and the 

 tendency to reproduce partially or completely the right 

 pelvic fin (i.e. that which is normally developed) in 

 reversed examples of Rhombosolea appears to be a similar 

 phenomenon. 



To summarize the above; of the seven known 

 examples of Rhombosolea with two pelvic fins, six at 

 least are definitely abnormal in other respects, four being 

 ambicolorate and two reversed. The development of two 

 pelvic fins in ambicolorate examples is to be regarded 



11 The type of this species is said to have been deposited in the 

 Natural History Department, University College, Dundee. Prof. J. 

 F. Gemmill, F.R.S., has kindly made a thorough search for the 

 specimen, but has failed to find it among the collections. 



'-'Bull. Mus. Comp. Zool., XL, 1903, pp. 219-242. 



