II. SUPPOSED EVIDENCE OF MUTATION IN MALTHOPSIS. 



Among the collection made by the ''Investigator" are four small communities 

 of pediculate fish of the genus Malthopsis, from separate but not far distant stations 

 in the Andaman Sea. 



It has been the custom in the Indian Museum to regard these four communities 

 as of one species — M. lutea — although the individuals are so variable that if certain of 

 them had been found alone in separate localities they would have been regarded 

 without doubt as distinct species. However, they have been looked upon as one 

 species, partly because each group was taken at one cast of the trawl in similar circum- 

 stances, every individual being of the same remarkable yellowish pink colour ; but the 

 fact that individuals of a particular and constant type occurred in the first three 

 communities obtained, was probably the chief reason for regarding the whole collection 

 as one species. This particular type predominated in the first community and it was 

 described and figured as the type of the species. It was at first thought that the great 

 variation shown by some members of the first community was due to the fact that 

 they were immature. It was subsequently made clear, when the other communities 

 were obtained, that the characters which were at first thought to be due to immaturity, 

 occurred in some adult forms. There are twenty-one specimens in all and it will be 

 shown that there are five distinct types among them not linked by intermediate forms. 

 The four communities will be designated by the letters A, B, C and D, the five types 

 by the letters v, w, x, y and z. The types are distributed in the following way; the 

 figures indicate the numbers of individuals of each type : — 

 Community A contains 2 v, 2 w, x. 

 ,, B ,, V, 6 w. 



,, C ,, V, w, 2 y. 



,, D ,, 3 w, 2 z. 



Type V occurs in three of the communities, while w occurs in all four. A speci- 

 men of type V was figured as M. lutea, for this type predominated in community A, 

 which was the first to be obtained, and from which the genus and species were 

 defined. 



Two years ago I drew up a description of the type z under the name 

 Malthopsis triangularis. There is no doubt that this type, of which there are two 

 specimens, is remarkably different from the type v. The description is pubHshed 

 here (antea) for the first time, though it seems that the other types w, x and y have 

 almost as good a claim to specific rank. 



