20 NATURAL HISTORY OP 



The order Gymnol^mata includes those forms in 

 which the lophophore is orbicular or nearly so, and the 

 epistome is wanting-. This order includes all the marine 

 forms and the fresh-water genus Paludicella. The 

 group Entoprocta contains the single order Pedi- 

 CELLiNEA. The sub-class Pterobranchia contains the 

 order Podostomata, with its single family Rhabdo- 



PLEURID^. 



It will be well here to explain what is meant by the 

 Bathymetric distribution of Zoophytes. Forbes has 

 laid down certain zones of depth into which the sea 

 may be divided, so as to indicate the area of occurrence 

 of organic life. It must, however, be premised that 

 the statements as to occurrence in certain zones are 

 only approximately true, as many species are found in 

 more than one zone. The four zones into which the 

 waters surrounding our coasts are divided are — the 

 Littoral zone, which extends between the levels of tbe 

 ebb and flood of ordinary tides ; the Laminarian zone, 

 extending below the littoral zone to the area only 

 uncovered at spring tides ; the Coralline zone, extend- 

 ing from the laminarian zone to a depth of 50 fathoms; 

 and the Deep-water zone, which underlies this to a 

 depth of 100 fathoms. To these zones Prof. Allman 

 adds the Surface zone, which comprises the area 

 extending to a depth of two or three feet below the 

 surface of the sea, where the medusae of the various 

 Hydroids abound in countless myriads. 



The principal species of Zoophytes are distributed 

 bathymetrically as follows :* — 



Littoral zone. Clava squamata, G. multicornis, 



* Alder, Cat. of North, and Dur. Zoophytes. Allman, G^'m, 

 Hyd., 107. 



