202 CRUSTACEA 



actual identity of species in several cases, e.g. Pacliycheles imna- 

 mensis and Hippa emerita, and the same thing has been observed 

 for the marine lish. 



Another connexion, at any rate during early tertiary times, 

 which proljably existed between now isolated tropical coasts, was 

 across the Atlantic from the West Indies to the Mediterranean 

 and West African coasts. Numerous facts speak for this 

 connexion. Species of Falinurus and Droviia occur in the West 

 Indies and the Mediterranean, whicli only differ from one another 

 in detail, and a connexion between these two regions has been 

 urged from the minute resemblances of the late Cretaceous Corals 

 of the West Indies with those ttf the Gosau beds of S. Europe, 

 and also of the Miocene land-molluscs of S. Europe with those at 

 the present time found in the West Indies. 



To account, then, for the present distribution of littoral 

 Crustacea we must imagine that great changes have taken place 

 during comparatively recent times in tlie coast-lines of the ocean, 

 but the guiding principle in both the past and present has been 

 temperature, and this factor enables us, despite the immense 

 changes in the configuration of the globe that must have taken 

 place, tQ divide the coasts latitudinally into Arctic, Antarctic, 

 and Circumtropical zones. 



Pelagic Crustacea belong chiefly to tlie Copepoda (Calanidae, 

 Ceutropagidae, Candacidae, Pontellidae, Corycaeidae), a few Ostra- 

 coda (Halocypridae and Cypridinae), and among Malacostraca a 

 few Amphipoda (Hyperina), some " tSchizopoda," and among 

 Decapoda only tlie Sergestidae, if we except the few special 

 forms which live on the floating weeds of the Sargasso Sea, e.g. 

 the Prawns Virhius acumiyiatus and Latreutes ensiferus, and the 

 Brachyura Ncptunus sayi and Planes minutus. Besides these 

 Crustacea which are pelagic as adults, there is an enormous host 

 of larval forms, both among Entomostraca and Malacostraca, 

 which are taken in the surface-plankton. 



In dealing with the Copepoda we have already mentioned the 

 vast pelagic shoals of these organisms which occur at particular 

 times of the year, and have an important influence on fishing 

 industries. Anomalocera pattersoni (Fig. 27, p. 60) is a good 

 instance of this. It is a large Heterarthrandrian, about 3 mm. long, 

 with the body of a fine bluish green colour ; it has a remarkable 

 power of springing out of the water, so that a slioal has tlie 



