422 Mr. W. Thompson on the Irish Coregoni. 



gin more oblique in C. clupeoides-^; its scales very much 

 smaller ; outline of dorsal fin very different, the membrane in 

 this falling considerably short of the points of the rays, and 

 its outline from the longest ray to the extremity of the fin 

 being somewhat rounded. This comparison was made be- 

 tween two specimens of C. clupeoides ? from 4 to 5 inches in 

 length, and two of C Willvghbeii about 6 inches long. 



From the continental species, Cor. Marcenula, as described 

 by Bloch, (and which, hke the C. Willughbeii, agrees with 

 that under consideration in the lower jaw being the longer,) 

 the C. clupeoides differs chiefly in having a greater number of 

 rays in the dorsal fin (14 or 15 to 10), in having teeth in the 

 under jaw, (on this difference alone I should not lay any 

 stress, the teeth being so small as to be easily overlooked,) 

 and in the negative character of wanting such an appearance 

 on the lateral line as would come under the description of 

 "garnie de cinquante-huit point noirs:"the scales on the 

 back and greater part of the sides are dotted with very mi- 

 nute black points visible under a lens, and of which those on 

 the lateral line have share, but not so many as the row just 

 above, the number of these points gradually decreasing from 

 the back dow^nwards. 



Should this fish eventually prove to be distinct from the 

 C. clupeoides of Nilsson, I would suggest that the specific 

 name of elegans be applied to it. 



Coregonus Pollan. Plate XVI. fig. 5. 



In connexion with the figure of C Pollan now given to ac- 

 company that of Cor, clupeoides, the following remarks are 

 offered. The characters in which the Pollan differed from 

 the two British species known at the time it was announced, 

 were pointed out in the original description. From the two 

 species since recorded, it may in the first place be stated to 

 differ from C. microcephalus, the Loch Lomond fish, in having 

 the head longer, the fins less, (and of a lighter colour,) and 

 the scales rather smaller; from the C. clupeoides the Pollan 



* The difference in this respect between these two species is not greater 

 than we sometimes see in different sexes of the same species of Salmo : the 

 Coregoni not having been dissected, tlieir sexes are unknown to me. 



