834 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



but the abdomen is less tumid than in the last stage. Specimens slightly older than 

 this are represented by Mr Couch (Brit. Fishes, vol. iii. pi. cli. and p. 113) as 

 Thompson's midge, and were referred by the late Dr Gray to the genus Coryphcena, 

 probably from the remarkable development of the ventrals. 



Specimens 1\ mm. longer than the last described, viz., 12*5 mm. in length, show a 

 large increase in the amount of black pigment on the dorsum, where it now gives rise 

 to a mottled appearance, extending over the sides and tail. Only a few corpuscles exist 

 near the ventral line behind the abdomen. The pectorals have increased in size and 

 strength, whereas the ventrals, though still of extraordinary dimensions, are now only 

 about one-fourth the length of the body, and are tipped with deep black, while the 

 remainder (|) of each fin is very pale in colour. The sides are silvery almost to the base 

 of the tail. In many of the specimens a parasite like a young Caligus projected from the 

 branchiostegal region. The youngest examples of Motella above described occurred in 

 32 fathoms water off the Isle of May, about 7 fathoms from the bottom, the others 

 were obtained in the same region in 25 fathoms water and about the same distance from 

 the bottom. 



When M. mustela reaches 24 or 25 mm. in length, the general silvery hue is marked, 

 only the dorsum of the head and body being brownish. The five barbels are distinct, 

 and the tips of the ventral fins do not project behind the pectorals, though their bases 

 have now advanced considerably in front of the former. The eye remains comparatively 

 large. The specimens of this size were obtained by the surface-net in Lochmaddy. 



At 29 or 30 mm. many of the adult characters have been assumed, the brownish- 

 black pigment having spread over the upper lateral regions. The tips of the ventrals 

 scarcely reach those of the pectorals, the three anterior rays being furnished with long 

 sensitive tips. The abdomen and lower lateral regions are silvery. 



The older Motellce obtained are characterised, as Mr Day observes,* by their very 

 bright silvery sides and dark bluish-black dorsum. The black axillary pigment occurs 

 in most of these, but it varies in intensity. They range from 26 to 40 mm. That 

 which most nearly resembles M. tricirrata possesses a pair of very short barbels or 

 papillse in the premaxillary region, but sometimes one is indistinct, and they probably 

 disappear during the subsequent stages. The ventrals extend about as far back as the 

 tips of the pectorals, but their bases are considerably in front of the latter, the second 

 ray being the longest of the three specially developed. All the black pigment has now 

 disappeared. Contrasted with M. mustela of the same length, the eye is somewhat 

 larger, and the space between them narrower, while the barbels are shorter. The first 

 dorsal appears also to be somewhat shorter (from before backward). The free rays of this 

 fin are characteristic in all the species. 



Two examples from the surface of the sea, south-east of the Isle of May, present 

 only a single median barbel on the upper lip. Both show axillary black pigment, and 

 in other respects correspond with the foregoing, except that the median barbel on the 



* Op. cit., p. 312. 



