Mr. W. Thompson on the Irish Coregoni. 423 



differs in being much larger, in the jaws being equal*, the 

 scales rather larger and in the form of the dorsal fin. (See ac- 

 companying figures.) 



Of a female Pollan, 11} inches in length, procured from 

 Lough Neagh on the 28th of November last, the entire 

 weight was 9 oz., that of the ova subsequently extracted 2 oz. 

 3 drachms ; of this, which was just ready for exclusion, I had 

 a drachm weighed, and reckoned the number of ova it con- 

 tained ; taking for granted that this would be alike in each 

 drachm throughout the whole, (and from the uniform size of 

 the ova, each a line in diameter, there can be very little dif- 

 ference,) the number of ova altogether would be 6156. This 

 too I should consider about the average produce of the spe- 

 cies, as the specimen was of ordinary size, and contained a 

 similar quantity of ova with several others dissected at the 

 same time. Of the stomachs, &c. of twelve Pollans examined 

 on this occasion, the greater number w T ere empty, but two or 

 three contained minute Entomostraca, two Pisidia, and a 

 Limnaeus pereger — this last was three lines in length. 



Jan. 1, 1839. I received from the Rev. C. Mayne a full- 

 grown specimen of the Cor, Pollan, taken near Killaloe, either 

 on the river Shannon or its expansion, Lough Derg. 



REFERENCES TO PLATE XVI. 



Fig. 1. Couchia minor. Fig. 2. Couchia argenteola. Fig. 3. 

 Couchia glauca. Fig. 4. Coregonus clupeoides. Fig. 5. Coregonus 

 Pollan. 



* This seems to be the best general character ; I have seen some indivi- 

 duals with the upper rather exceeding the lower jaw, others with the lower 

 slightly projecting beyond the upper, and the difference was not sexual. It 

 is perhaps unnecessary to observe, as it would apply to fishes generally, that 

 other individuals examined vary much in relative proportions from those 

 which served for the original description : the proportion of head to depth 

 of body, it is obvious, must vary in the sexes at particular periods ; that of 

 head to entire length I have found to be as 1 to 5, as well as "1 to 3^," and 

 the vertebrae 60. The two following characters were before unnoticed : 

 axillary scale of ventral fins about one-third their length — about 84 scales on 

 the lateral line : this is the number attributed by Dr. Parnell to both of the 

 Loch Lomond Coregoni ; in a specimen of one of these, C. microcephalics, 

 under 10 inches in length, (much less than the size they attain,) with which 

 I have been favoured by its describer, there are but 76 ? scales on this line. 

 This induced me to examine various sized Pollans, to see whether there 

 might be any difference in this respect, when none appeared in the indivi- 

 duals inspected, which were from 9^ to 13 inches in length. 



