420 
PACIFIC SCIENCE, Vol. IX, October, 1955 
stations, but they were examined to see 
whether either C. tenuicornis or C. lighti was 
present. In all samples examined C. tenuicornis 
was present, but no specimens of C. lighti 
were found. C. lighti appears to be limited to 
oceanic waters off the coasts of southern 
California and Baja California, while C. tenui- 
cornis occurs in neritic as well as oceanic 
waters, and has a much greater north-south 
range. Further information is needed con- 
cerning the distribution of C. lighti to the 
west of the area from which I have examined 
plankton samples. 
The type specimen of C. tenuicornis , unfor- 
tunately no longer extant, was taken at 40° 
N., 157° W. To assist in determining which 
of the two forms from the CCOFI cruises was 
Dana’s species, some of the plankton samples 
from stations of the "Northern Holiday" 
cruise of the Scripps Institution of Oceano- 
graphy in 1951 were examined. At the follow- 
ing stations only the smaller form (C. 
tenuicornis ) was taken; no C. lighti was found 
in the sample: 
"northern holiday’’ 
ytion 
LATITUDE 
LONGITUDE 
45 
42° 15' 
155° 36' 
46 
41° 20' 
155° 20' 
47 
40° 09' 
155° 03' 
48 
39° 18' 
154° 38' 
49 
38° 30' 
154° 25' 
50 
37° 28' 
154° 12' 
56 
28° 06.5' 
151° 25' 
This makes it highly probable that the 
smaller form is conspecific with Dana’s spec- 
imen. The more restricted range of the larger 
form (C. lighti ), which appears to be limited 
to an area not yet thoroughly explored, per- 
haps explains why it has not been discovered 
previously. 
DISCUSSION 
It might be argued that since the two forms 
discussed herein differ only in body size and 
conformation they do not merit specific dis- 
tinction. However, the available evidence in- 
dicates that they must be treated as different 
Fig. 4. Station positions of the CCOFI-Inter- 
American Tropical Tuna Commission Cruise, January 
1-March 4, 1953 in the east-central Pacific. Calanus 
tenuicornis was present in all stations; C. lighti was found 
at none. 
species, rather than as subspecies or environ- 
mentally determined forms of a single species. 
1. Although the geographic range of tenui- 
cornis overlaps extensively the more restricted 
range of lighti, each species is characterized 
by a distinct geographic range. 
2. The absence of specimens intermediate 
in size or in body form at stations where the 
two species occurred together is evidence that 
the two copepods are reproductively isolated. 
3. The two species differ in their pigmenta- 
tion. Preserved females of C. lighti have 
spherical spots of red pigment in the first 
antennae. These were not found in any pre- 
served female of C. tenuicornis , or in five living 
specimens brought to the laboratory from 
about three miles off Point Loma, California. 
It is possible that the two forms will be 
found to intergrade in other regions where 
their ranges overlap. Such a discovery might 
make it necessary to reduce C. lighti to sub- 
specific rank. For the present, however, it is 
given specific status. 
It is well known that the size and form of 
both marine and fresh-water copepods can be 
modified by environmental influences, es- 
pecially temperature. When reared in the lab- 
