1912] Esterly: Copepoda of the San Diego Region 333 
what conditions are held to be the more important in the char- 
acterization of species. As a matter of fact the species mentioned 
in the above speculation are two that we know practically nothing 
about (except as to structure), yet they may be used to illustrate 
the different points of view that are possible in the matter of 
‘coincident versus contiguous distribution.’’ 
The interesting matter of color of marine animals and the 
depths at which they occur has recently been discussed by Hjort 
(1911). It was found on the ‘‘Michael Sars’’ expedition that 
black and red forms predominate among animals from greatest 
depths (Hjort, 1911, pp. 503, 504), and in certain eases all the 
specimens of fishes caught above 150m. were taken at night 
(p. 505). Hjort states (p. 505) that the rays of light will have 
passed through the same distance to reach a depth of 500 meters 
in 50° N, that they will pass through to reach 650 meters in 33° N, 
or 300 meters in 67° N. The visible depth in the open sea is 
given as 50 meters in 33° N, 40 meters in 50° N, and 25 meters 
in 67° N. As to the intensity (p. 506), it will be the same from 
rectilinear rays in 33° N at about 200 meters, at 50° N at about 
500 meters, and at 67° N at about 200 meters. The red and black 
forms therefore have an upper limit in different waters which 
corresponds everywhere with the same intensity of light. The 
upper limit for the red crustacea at about 50° N was 500 meters 
below the surface, while for the same forms at 33° N it was from 
200 to 300 meters deeper. 
The distribution of the copepods of this region is in general 
line with the observations of Hjort. Many of the typically deep 
water forms are characterized by red or orange in the body as a 
whole or merely in localized regions. Such are the species of 
Euchaeta like tonsa; of Euchirella such as galeata, pulchra, 
simplex, propria, truncata; Pleuromamma quadrungulata; others 
might be given as examples of deep water forms that have red or 
orange-red pigment. On the other hand there are species with a 
similar range which are exceedingly transparent, such as Augap- 
tilus lucidus or pyramidalis; the former has a brown spot around 
the mouth while the latter is entirely without pigment. It is 
hardly necessary to mention Calanus finmarchicus or Eucalanus 
elongatus which have been taken as deep as 400 fathoms with the 
