236 NATURAL SCIENCE. April, 



Of the thirteen species of the sub-family in the Pacific distinguished by 

 Jordan and Goss, it occurs in eight, and it also occurs in one genus 

 in the Pacific in the quite distinct sub-family, Hippoglossinae. 

 These species differ considerably in habits and stations, and there is 

 no indication that they possess one common habit or peculiarity 

 of life to which this branching of the lateral line is adapted or 

 related. There may be something in the Pacific Ocean which tends 

 to produce this branching of the lateral line. It seems to have been 

 independently produced more than once in separate lines of descent. 

 We have no reason whatever to suppose that it is useful to the species 

 that have it, and would not be useful to those that are without it. As 

 systematists, Jordan and Goss use this character in uniting those 

 species of Platessinae that possess it ; but examination of the other 

 characters rather favours the view that it is a subordinate character, 

 some of the species that have it being more closely allied to Atlantic 

 species without it than to other Pacific species that possess it. It is 

 difficult among the many cross-resemblances that occur to trace with 

 any confidence the lines of divergent descent among these species, in 

 other words to found the systematic arrangement on genealogical 

 ideas. I prefer to leave these species and take up the consideration 

 of the species allied to our plaice and flounder. 



Leaving other characters aside, the plaice (Pleuvonectes platessa) is 

 distinguished from L. limanda by wanting the arch to the lateral line, 

 by having reduced cycloid scales, and tubercles on the post-ocular 

 ridge. The flounder has differentiated scales, most of them being 

 reduced and cycloid as in the plaice, but those along the bases of the 

 longitudinal fins, along the lateral line, and on the head being enlarged 

 to form rough spiny tubercles. We have seen that the dab has a 

 relative on the west side of the Atlantic, and another in the North 

 Pacific. Pseudopleuronectes americanus, the representative of the plaice 

 on the east coast of America, approaches the dab in having im- 

 bricated ctenoid scales. In Liopsetta putnami the spinulation of the 

 scales is a secondary sexual character, the scales in the male being 

 rough and strongly ctenoid, in the female smooth and almost 

 completely cycloid. 



Now, of Liopsetta only one species is adequately known ; it 

 ranges from Cape Cod to Labrador, and is rather common. It is 

 perfectly distinct from the plaice, and yet Mr. Holt has just described, 

 in the Journal of the Marine Biological Association (vol. iii., no. 3), a 

 local race of the plaice which distinctly approaches to the condition 

 of Liopsetta putnami ; the latter is therefore a more perfect American 

 representative of the plaice than is Pseudopleuronectes. Mr. Holt's 

 specimens came from the Baltic. They were much smaller than the 

 North Sea plaice, the female being mature at 9^ to 13^- inches in 

 length, and some of them were more or less ' ciliated,' that is to say, 

 the scales were more or less ctenoid. This character of the scales 

 was not uniformly developed, but most marked on the head and 



