514 ON THE FAUNA AND BOTTOM-DEPOSITS NEAR THE SO-FM. LINE 



the distribution of the fishes on all the grounds in the Plymouth district, 

 and those met with in the present investigation, which were for the 

 most part identified by him, will be included in his general account. 

 For the Geographical Distribution, as given in Table VI., I have 

 relied on Smitt's Scandinavian Fishes and on Giinther's British Museum 

 Catalogue. 



Section VII. 

 GENERAL CONSIDERATIONS. 



The Association of Species with one Another. In the descrip- 

 tions of the grounds investigated, as well as in the accounts of the 

 distribution of individual species, numerous instances of the definite 

 association of one species with another have been pointed out. Many of 

 these are examples of the kind of association which is already well 

 known, e.g., Sagartia parasitica with Eupagiirus Bernhardus, Adamsia 

 palliata with Eupagurus Prideauxii, Montacuta suhstriata with Spaiangus 

 purpureus, etc. Others, such as the frequent association in one group of 

 Thclepus sp)., Sertularella Gayi, Ascidiella scabra, and Sahella {pavonina ?) 

 (cf. p. 390), or of Chaetopterus variopcdatus, Halecium halecinum, Plumu- 

 laria Gatharina, etc. (p. 414), have not been previously described in 

 detail, and are probably of a less definite nature. It will be of 

 interest and importance not only to compare such groups with those 

 found in other localities, but also to compare the whole fauna found 

 upon similar bottom-deposits in different districts. Unfortunately the 

 published data upon which any such comparison can be founded are 

 neither numerous nor altogether satisfactory. The most promising 

 reports from which the general nature of the fauna at particular spots 

 can be ascertained are those giving the results of the dredgings and 

 trawlings of the German expedition in the Pommerania, which worked 

 in the North Sea in 1872 and 1873. In these the numbers of the 

 stations at which each species was obtained are given, and by working 

 through the reports of the specialists in each group one can compile 

 a list of the fauna at any particular station. Unfortunately there is 

 a good deal of internal evidence to indicate that, in the case of the 

 more common species especially, the list of stations at which each was 

 taken is by no means complete, and the lists of the fauna obtained 

 at particular stations derived from the reports are, therefore, not as 

 perfect as could be desired, nor can one be sure that the common 

 and prevailing species are mentioned. 



I give below the lists for five stations where the fauna was evidently 

 in many ways similar to that found on some of the Eddystone Grounds. 



