liv INTRODUCTION. 



changes in the forms that the animals of this genus 

 undergo in their growth to an adult state, it is not im- 

 probable that immature specimens may be misinterpreted 

 for adult varieties. Cyamus lives parasitically on the 

 whale, and probably thrives on no other animal. The 

 one or two solitary specimens that have been found 

 attached to the dolphin are probably young creatures that 

 have strayed from their natural habitat. 



The genera of Isopoda appear to be more generally 

 diffused throughout the various regions of the sea ; and 

 from the various distant localities in which that species 

 have been found, some may be inclined to think that 

 they are universally distributed. 



The genus Tanais has been found on the coasts of 

 North-Western Europe, Brazil, in the Zooloo and Feejee 

 seas, as well as on the western coast of North America ; 

 and equally varied have been the recorded habitats of the 

 nearly allied genera, Paratanais and Leptochelia, which 

 latter Fritz Miiller believes to be the male of Tanais. 

 The near ally, Apseudes, is only known in Europe and 

 Egypt, where but few specimens of two closely resem- 

 bling species have been found. The genera Anthura and 

 Paranthura are also sparsely represented, both in the 

 species and specimens. They have been taken on the 

 southern and western coasts of Europe, at New Zealand, 

 the Mauritius, and the Cape of Good Hope, as well as on 

 the eastern coast of North America. Of the genus Anceus, 

 of which eleven species have been determined on the 

 north-west coast of France, by M. Hesse, three at most 

 are known to the rest of Europe, and but a single species 

 to the eastern coast of North America. 



The Bopyrida are tolerably abundant in the temperate 

 regions, but few in the more tropical or Arctic latitudes, 

 the genera confining themselves with considerable exacti- 

 tude to peculiar species of Crustacea. Thus we have failed 



