MARINE FISHES. 207 



small scales, and they are continuous with the upper margin of the opercular fold. The 

 scales are peculiar ; the projecting margins are thickly covered with skin, and on the 

 head, on the blind side of the body, these integumentary margins become thicker and 

 might be regarded as short tentacles. The scales are continued on both sides of the 

 body for a short distance into the gill cavities. 



Psettyllis pellucida, Alcock. 

 Palk Bay, 3 specimens, 1*3 inches to 1*6 inches. 



Psettyllis ocellata, Alcock. 



Palk Bay, 7 specimens. 1*6 inches to 2*2 inches, and a mature female, 47 inches 

 long the latter is figured (Plate I., fig. 3) as only an immature stage was known. 



Note on the genus Psettyllis. Plate I., fig 3, and Plate II. 



Psettyllis was created by Alcock (1) in 1890 for the reception of a number of 

 Pleuronectids allied to Khomboidichthys which he obtained off the Ganjam and 

 Vizagapatam coasts in 7 to 13 fathoms of water. Alcock entertained the possibility 

 that these forms might be "larval or stunted" flat-fish; but in the relative 

 proportions of the body, the completed symmetry, the unilateral restriction of the 

 pigment, the perfect ossification of the skeleton, the slight unilateral atrophy of 

 the paired fins, and the character of the vertical fins, he saw indications of develop- 

 ment which warranted generic and specific discrimination. Many of these characters 

 are not, however, absolutely diagnostic of completed development ; the ossification of 

 the skeleton, for instance, is already almost perfect in very small plaice, and some 

 pigmentation of the blind side would appear to be tpiite a normal feature in some 

 tropical species of Pleuronectidse, in some species of Amoglossus for instance. Study 

 of the specimens of Psettyllis obtained by Professor Hehdman in Palk Bay affords 

 conclusive proof that the forms described by Alcock as P. ocellata are certainly, and 

 that those described as P. pellucida are probably, immature. 



The 8 specimens of P. ocellata (Plate II., figs. 3 to 8) form a natural series and 

 have the following characters in common : (l) The pigmentation, in so far as the 

 form and distribution of the ocelli are concerned: there is a most characteristic 

 ocellus behind the lateral line elevation and a number of differently shaped ocelli on 

 the body and vertical fins; (2) the lateral line: there is a peculiar elevation above 

 the pectoral fin on the ocular side, which presents two almost right angles ; and 

 (3) the scales : the surface of the body is covered with small cycloid scales, but close 

 to the bases of the dorsal and anal fins on the ocular side there are one or more rows 

 of ctenoid scales. 



Two of these specimens belong to the stage figured and described by Alcock. 

 The general surface of the body is colourless ; the eyes are separated by an inter- 

 orbital space equal to 17 times the major diameter of the eye ; the scales are very 



