Mr. W. Thompson's Additions to the Fauna of Ireland. 241 



adult, as were the specimens taken, the largest exceeding 1£ inch in 

 length from point of anterior scales to end of the caudal plates. 



Mr. J. V. Thompson remarks that M. chamceleon " has never been 

 observed like the other species in any great numbers together, but 

 scattered and solitary, often associated with M. vulgaris," p. 29. 

 But where they came under my observation in this instance, a small 

 arm of the lough a few feet in depth presented the extraordinary 

 spectacle of being quite alive with them. They were all swimming 

 in one direction, towards the sea, and moving regularly and hori- 

 zontally onward. 



It is difficult, owing to the figure being deficient in elaboration, to 

 judge whether or not Montagu's Cancer astacus multipes, Linn. 

 Trans, ix. (p. 90) pi. 5. f. 3, be this species, but I agree with Mr. J. 

 V. Thompson that the Cancer fleocuosus, Mull. Zool. Dan. vol. ii. 

 p. 34. pi. 66, is so. M. Edwards (Hist. Crust, vol. ii. p. 458) ob- 

 serves, that spines are represented on the sides of the abdomen in 

 Midler's figure of M. flexuosus, but although such an appearance is 

 presented in the plate, surely it is the mere setae of the subabdominal 

 fins which are intended to be represented. The specimens taken on 

 this occasion were all of one hue, as the millions in the water seemed 

 to be ; this was a very pale olive or " pellucid cinereous," as ascribed 

 to the M. Leachii by Mr. J. V. Thompson, from which they differed 

 only in having black instead of " reddish rust-coloured" spots. Each 

 segment of the body in every specimen examined (about thirty in 

 number) is marked with a round black spot, whence, in some, arbo- 

 rescent arms branch off ; in others there is no arborescent appearance, 

 but the segment is dotted regularly over with extremely minute 

 points. To 



Mysis vulgaris, J. V. Thomp. ibid. p. 30. pi. 1, 

 my attention was first directed by remarking among those captured, 

 individuals wanting the black spot on the segments of the body, 

 when, singling out three of these, they proved to be of this species — 

 all the others were M. chamceleon. The segments however exhibit an 

 arborescent veining, though wanting the black central spot. These 

 specimens are one inch in length, or one-fifth less than the largest 

 M. chamceleon taken with them. If the proportion of the one species to 

 the other in the myriads seen were as in those taken, the numbers of 

 M. vulgaris to the other were but as one to ten. Some of these 

 (M. vulgaris) produced young in the phial, like those represented 

 by M idler in the ' Zoologia Danica,' pi. 66, and by Kroyer in the 

 ' Voyages Scandin. et Lapon. Crustaces,' pi. 9. 



Bally home, Belfast bay, July 4, 1846. From the rocks at the 

 entrance of this bay I captured in pure sea-water a number of the 

 Mysis of various sizes, all of which proved to be M. chamceleon. 

 The extraordinary difference in colour of these specimens, all taken 

 together within the space of a few yards, well justified the specific 

 name. They were brown, green, pink, red, and hyaline, some as 

 transparent in colour as the water itself : a few displayed a whitish 

 longitudinal stripe down the back. With the view to a more par- 



