I. '08. 88 



every year,^ and it has also been observed in other places. 

 Murie (1903) gives a good account of it in his Eeport on the 

 Sea Fisheries of the Thames Estuary. 



Although these migratory movements have not so far been 

 noticed on the Irish coast, there is no reason to suppose that 

 the habits of Irish specimens are in any essential way different 

 from those on the east coast of England. The migrations in 

 any district must be largely dependant on the nature of the 

 sea bottom and the presence of a good food supply. Tnbi- 

 colons polychaetes, more especially Sahellaria alveolata, are a 

 favourite food of this species. 



Wollebaek has recently (1908) brought to light a very in- 

 teresting feature of P. Montagui. Caiman in 1896 showed 

 that in the male two different forms of the endopod of the first 

 pair of pleopods exist, and Wollebaek has been able to identify 

 these with the breeding and non-breeding phases of the species. 

 In the autumn months (at the commencement of the breeding 

 season) this endopod is provided with a sharply pointed ter- 

 minal process and the appendix masculina on the second pair 

 of pleopods is fully developed and furnished with setae ; in 

 spring and summer the appendix masculina is greatly 

 diminished or wholly absent and the process on the endopod 

 of the first pair of pleopods is shrunken and blunted. 



This is the only instance^ in which an alternating 

 dimorphism has been demonstrated in Decapoda Natantia ; 

 among Eeptantia, phenomena of an analogous nature are 

 known in Camharus and in certain Oxyrhyncha. 



General distribution. — From the extreme north of Norway 

 to the English Channel. The species is abundant over the 

 whole of the North Sea and is found in the Skagerrak, Catte- 

 gat and Baltic. It is common off the English and Scotch 

 coasts, and has been recorded from the Shetlands. It is 

 known from the White Sea (Birula), Iceland (Sars), Rockall 

 (Caiman), and W^. Greenland to lat. 69° 14' N. (Hansen) ; it is 

 plentiful off the east coast of N. America as far south as lat. 

 41° 25' N., and has been found in Baffin Bay (Hansen). In 

 the Pacific it has been recorded from the Bering Sea (Richters) 

 and southwards along the American coast to Point Arena, 

 California (Eathbun). The majority of the Pacific specimens 

 have been referred to the var. tridens, 



Irish distrihution . — Off the east coast P. Montagui is abund- 

 ant inside the 30-fathom line, but is scarcer m deeper water. 

 In the south it is apparently quite rare ; I know of only one 

 record— from the vicinity of Ballycotton (Dublin Museum). 

 In the west the species does not seem common, but it has 



1 The Humber shrimp -trawlers know quite well that the appearance of 

 *' green bellies," i.e., ovigerous females, is a sign that the prawns will 

 soon be off to sea. 



2 Wollebaek, strangely enough, was unable to. discover similar pheno- 

 mena in other species of Pandalus, 



