42 NATURAL HISTORY OF 



favourable until tlie evening, when between 9 and 10 p.m. 

 it suddenly shifted to N.W., dying away to northward 

 on the morning of the 15th, and soon after springing up 

 from the S.W. Sail was accordingly shortened, and the screw 

 again brought into requisition, the breeze meanwhile freshen- 

 ing with such rapidity, that by the afternoon it was blowing 

 hard, with heavy squalls and a heavy sea from the southward, 

 so that we laboured on under steam, the vessel rolling and 

 pitching violently. The gale continued during the next two 

 days, accompanied with thick, gloomy, drizzling weather, and 

 a few large albatrosses and many stormy petrels were seen ; 

 but by the morning of the 18th it ceased, and was succeeded 

 by a favourable wind, which permitted us to proceed under 

 sail alone. We took advantage of this circumstance to em- 

 ploy the towing-net, by which we procured some specimens 

 of a bright blue Isopodous crustacean, the Idotea annulata of 

 Dana. Mr. Spence Bate, to whose kindness I am indebted 

 for information regarding this and other species of Crustacea 

 submitted to him, remarks that the blue colour appears to be 

 a peculiarity of pelagic species,* and mentions that he has 

 received specimens of the same animal " from Dr. Wallich,'* 

 who says, " it is a parasite on Physalia, almost invariably at- 

 tached to the float," and that Dr. Wallich's specimens were 

 taken between the Bay of Bengal and the Cape of Good Hope, 

 while those on which Dana founded the species were taken in 

 the Antarctic seas, south of New Holland. The Idotea annu- 

 lata, therefore, enjoys a wide geographical range. I took it 

 again the next season to the south of the river Plate ; and I 

 may remark, that I never found it associated with Physalia, 

 or any other oceanic hydrozoon. 



* Our commonest British species, which is to be met with plentifully on 

 stones and among fuci at low water, is of a dull greenish hue. 



