140 Prof. M'Intosh on the 



The class Crustacea, as a rule, exceeds most of the other 

 groups in the abundance and variety of its pelagic adults and 



Selagic larva3. The tow-net, indeed, off the eastern shores in 

 uly and August is sometimes coated with a semisolid mass 

 of their bodies, consisting of young cirripedes, copepods, larva3 

 of the common shore and edible crabs, porcelain crabs, and 

 others, such as the common and Norway lobsters. These larvae, 

 as they descend to the bottom in their more advanced stages, 

 may be reckoned as the fauna of all intermediate regions. 

 Moreover, pelagic life is not confined to the larv£e, for the 

 eastern bays occasionally swarm with such schizopods aa 

 Thysanoessa tenera, G. O. Sars, and Nyctiphanes norvegica, M. 

 Sars — Norwegian types discovered by the authors mentioned, 

 the former being already known as British, while the latter, 

 Dr. Merle Norman kindly informs me, for the first time appears 

 on our list. Both forms occurred ofi' the east coast, and especially 

 in St. Andrews Bay, towards the end of April, and so densely 

 that the tidal wave was crowded with them, and miles of sand 

 were strewed with their bodies which the receding wavelets 

 left in streaks and curves*. Various sessile-eyed crustaceans 

 also occasionally occur at the surface, such as Amjyhithoe^ 

 Lestrigonus^ Lystanassa, besides many Ostracoda and the 

 young of Diastylis. Moreover the young of Caligus are 

 sometimes in great abundance oflF rocky margins, and thus are 

 ready to settle on the various food-fishes, none being more 

 liable to attack than the cod. 



Amongst the Molluscoida the ciliated larva3 of the Polyzoa 

 and the tailed larvee of many tunicates increase the pelagic 

 fauna, especially in rich inshore regions ; while Appendicu- 

 laria is frequent in the tow-net both there and in the open 

 sea. The eastern coast, however, presents a great conti-ast to 

 the western in the entire absence of Salpas, the chains of which 

 sometimes occur in countless multitudes in the warm Gulf- 

 stream bathing the Outer Hebrides. 



The larval Mollusca are generally pelagic, and this is espe- 

 cially the case with the bivalves which inhabit sandy flats. 

 Few, moreover, have any conception of the enormous num- 

 bers of the larval mussels alone which are poured into the 

 various bays and the water beyond every year ; though an 

 idea of their abundance may be obtained by inspecting the 

 solid mass which they form in the tow-net, or the rocks and 

 zoophytes {Obelia, Gemellana, &c.) at a somewhat later 

 stage when assuming a sedentary existence. The pteropods 

 {Spinalis) of the eastern waters, again, are pelagic throughout 



* When dried they closely resembled chafl^ for which, indeed, the un- 

 initiated took them. 



