V. NOTES ON INDIAN FISH. 



By R. B, Seymour Sewell, B.A., Capt., I. M.S., Surgeon- 



Naturalist to the Marine Survey of India; Hon. Assistant^ 



Zoological Section, Indian Museum, Calcutta. 



(Plate VIII.) 



I. — Notes on the Genus MaltJwpsis. 



This genus was created by Wood-Mason and Alcock for a new 

 species of deep-sea fish obtained by the R.I.M.S.S. '' Investigator" 

 in the Andaman Sea. 



As has previously been pointed out (Lloyd, 1909-10, p. 171), 

 the collection in the Indian Museum, Calcutta, contains two 

 forms which differ very considerably in size and other characters, 

 and the original description by Wood-Mason and Alcock (1891) 

 applies only to the larger form ; possibly they thought that the 

 smaller form was merely an immature stage. Further examples 

 of the smaller form were subsequently obtained from the same 

 region and a full description was published by lyloyd (loc. cit., 

 1909-10) under the name Malthopsis triangularis : in the second 

 part of the same paper, however, this author assumes that both 

 these forms are in reality members of the same species and, 

 arguing on this assumption, proceeds to demonstrate "^^ supposed 

 evidence of mutation. " Recently Lloyd (1912) has reiterated his 

 views on this supposed evidence: as he himself shows, the indivi- 

 duals of this genus in the present collection can be divided into 

 two groups by the difference in the arrangement of the dermal 

 scutes and the form and degree of development of the opercular 

 spine — groups that he terms "orderly" and "disorderly" res- 

 pectively. In both forms very considerable differences are to be 

 found in the breadth of the disc proportionally in proportion to the 

 total length, but such differences are only to be expected in cases 

 where the disc is, as in the present case, supported by flexible 

 bony arches and must largely depend on the degree of external 

 pressure and muscular contraction existing at the time of death. 

 As I have elsewhere shown (Sewell, Rec. Ind. Mus., vol. VII, p. 8, 

 Calcutta, 19 12), similar variations are to be found in examples of 

 the closely-allied species Halicmetus ruber, Alcock. 



I have recently had occasion to re-examine the collection and 

 r have no doubt that it contains two absolutely distinct species, 

 the chief structural characters of which I give below: — 



