202 CRUSTACEA CHAP. 
actual identity of species in several cases, e.g. Pachycheles pana- 
mensis and Hippa emerita, and the same thing has been observed 
for the marine fish. 
Another connexion, at any rate during early tertiary times, 
which probably 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 Palinwrus and Dromia occur in the West 
Indies and the Mediterranean, which 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 of the Gosau beds of 8S. Europe, 
and also of the Miocene land-molluses of 8. 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 the 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, to divide the coasts latitudinally into Arctic, Antarctic, 
and Circumtropical zones. 
Pelagic Crustacea belong chiefly to the Copepoda (Calanidae, 
Centropagidae, Candacidae, Pontellidae, Corycaeidae), a few Ostra- 
coda (Halocypridae and Cypridinae), and among Malacostraca a 
few Amphipoda (Hyperina), some “Schizopoda,’ and among 
Decapoda only the Sergestidae, if we except the few special 
forms which live on the floating weeds of the Sargasso Sea, e.g. 
the Prawns Virbius acwminatus and Latreutes ensiferus, and the 
Brachyura Neptunus 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 isa 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 shoal has the 
