THE PLUMULARID/E. 



49 



riant marine fauiia. Both are extensive archipelagoes with numerous islands, between which 

 strong, warm currents are forced by the winds and tides a very important factor, as Alexander 

 Agassiz has pointed out. Both are characterized by extensive coral reefs with their attendant 

 profusion of marine organisms of many kinds, and both contain great areas of comparatively 

 shallow seas, affording what are probably the most favorable conditions for the Plumularida-. It 

 also seems likely that the presence in these regions of land masses of considerable magnitude is 

 a factor which is favorable to the production of luxuriant marine life. 



Representatives of this family have been found in considerable abundance down to nearly 300 

 fathoms, and not uufrequently to 500 fathoms. They have occasionally, however, been found at 

 greater depths, as follows: Flumularia attenuata Allman, 576 fathoms, Blake; Cladocarpus for- 

 mosits Allmau, 775 fathoms, Challenger; Gladocarpus pectiniferus Allman, 000 fathoms, Chall-engei-; 

 Gladocarpus flexuosus Nutting, 910 fathoms, Albatross; Aylaophenia lopliwnrpa Allman, 1,181 fath- 

 oms, Albatross; Aglaophenia crenata Fewkes, 1,242 fathoms, Jilakr; Ag^aophenopsisverrilli'NvLttiag, 

 1,497 fathoms, Albatroxx; At/laphf,nopitin rcrrilli Nutting, 1,742 fathoms, Albatross. 



In the bathyuietrical tables given by Sars ' and others the zones are of unequal vertical thick- 

 ness. Sars divides the depth down to 300 fathoms into the following zones: 0-10, 10-20, 20-50, 

 50-100, 100-150, 150-200, 200-300. 



This method is useful where a limited number of species and comparatively few dredging sta- 

 tions are included, and I have adopted a similar arrangement for the bathyuietrical distribution of 

 genera in this work. When, however, a considerable number of species is included and a suffi- 

 cient number of stations occupied at various depths to allow of an attempt at adducing conclu- 

 sions concerning the general subject of bathyrnetrical distribution, it is better to have the zones 

 more numerous and of equal vertical thickness. For this reason the tables for the whole groups 

 of Eleutheroplea and Statoplea are founded on equally dividing the whole depth down to 500 

 fathoms into ten zones of 50 fathoms each. 



The data upon which the following table is constructed seem sufficient to furnish at least a 

 reliable indication of bathy metrical distribution down to 500 fathoms. In general it may be said 

 that there is an apparent decrease in the number of species with the increase in depth. There 

 are two exceptions to this rule, one in the Statoplea, where five species are found at a depth of 

 from 350 to 400 fathoms and seven species at a depth of from 400 to 450 fathoms; the other is in the 

 Eleutheroplea, where seven species are found at a depth of from 200 to 250 fathoms and thirteen 

 species between 250 and .'U)0 fathoms. In both cases, however, it will be noted that not more than 

 one species was found in the next zone, indicating possibly an insufficient or unfortunate explora- 

 tion of these latter zones, or particularly rich hauls in the preceding zones. It will also be noted 

 that these breaks are not at the same depth for the two groups, which would also indicate that the 

 departure from the rule given above was due to accidental causes. 



[The abbreviations are used as follows : N. Atl., North Atlantic coast of America from Charleston northward. W. I., Atlantic coast of 

 North and Central America south of Charleston, and the West Indies. S. Atl., South Atlantic, counting south of the Isthmus ol Panama. 

 Eu., European shores of the Atlantic. N. P., North Pacific southward to Panama. S. P., South Pacitic south of Panama. Aus., Australian and 

 East Indian region.] 



Bathyrnetrical distribution of American Plumularida: 



ELEUTHEROPLEA. 



12833- 



1 Bidrag til Kundskabeu om Norges Hydroider, 1873, pp. 44-48. 



