THE PLUMULARID.E. 

 Bathtjnu'triml tlixtribntion <;/' American Plion itlitriilir Continued. 



STATOPLEA Coutinnetl. 



51 



The preceding table, while useful in showing what might be called qualitative distribution in 

 depth and in indicating the distribution of individual species, can not be depended upon to show 

 the quantitative distribution of species. It would, on the face of it, seem to indicate that the 

 number of species decreased regularly with the depth. This is in accord with the generally 

 received ideas concerning bathymetric distribution. A little consideration, however, will show 

 that there is an element of error involved which utterly invalidates the showing of this and, so far 

 as I know, all other published tables on bathymetrical distribution, inasmuch as these zones have 

 been eery unequally e.rploretl. If one hundred hauls of the dredge have been made in one zone and 

 only ten in another, the number of species actually found in the nrst may be several times that found 

 in the second, and yet the second may be in reality a much richer zone. It will thus be seen that 

 the preceding table is, as it stands, of no value whatever as an index of the relative richness of the 

 several zones. In order to obviate this defect I have, with the help of my father, reduced to 

 tabulated form 2,660 dredging stations recorded in American waters down to r>00 fathoms, 1 so that 

 the number of hauls made in each vertical zone of 50 fathoms is indicated. Knowing, then, the 

 actual number of stations in each zone and the actual number of species secured, it is easy to 

 construct the following table: 



'This was made possible by the use of the excellent Lists of Dredging .Stations ill North American Waters, etc., 

 compiled by Saudereou Smith, 1888. 



