232 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
series of observations has been made on. the area northeast of a line drawn from 
San Francisco to Unalashka Island. The chief oceanic current in this area is the 
enfeebled remnant of the Kuro Siwo and its deflected northerly and southerly 
arms. A drift of Arctic water southward is noticeable near the passes between 
the Aleutian Islands. The latter brings Clione and Limacina from Bering Sea, 
and the latter genus reaches, on the southerly arm, or coastal current, sometimes 
as far south as Monterey, California. 
The Kuro Siwo is at the height of its strength and temperature in the early part 
of September in this region. Its surface water 300 miles off shore sometimes 
rises as high as 68° Fahrenheit, though the heat is rapidly given off to the atmos- 
phere after the coast is reached, and the southerly arm off San Francisco has a tem- 
perature of only 54° Fahrenheit. The warm belt is never more than fifty miles 
in width in the area in question. The current is imperceptible, as such, in winter 
and early spring, when one encounters only northern pteropods. At this season, 
and well up to July, no pteropods of the genera Cleodora, Cavolina, Pneumoder- 
mon, and Corolla were taken north of latitude 389. After this time the Kuro 
Siwo water begins to be noticed in the temperatures, and the forms mentioned are 
. more or less prevalent in small swarms. In September they exist in great abun- 
dance, brought in the warm water as far north as latitude 50? and less abundantly 
to latitude 54°, 
The Cavolina, Cleodora, and Pneumodermon are apt to appear (when present 
in the area) at the surface during calms, especially if the sun be overcast. The 
last mentioned genus is particularly noticeable from the disturbance caused by 
the rapid movements of its large and powerful flippers. Its motions recall those 
of humblebees over a field of clover. Ifa breeze of any strength springs up, the 
pteropods sink to'a calmer stratum. I am unable to say positively that they are 
habitually crepuscular, but it is a fact that my largest hauls have been made 
about sundown. These animals are not equally distributed over the sea, but are 
distinctly gregarious, occurring in large swarms, which are trailed out into long 
bands by the action of the winds. Adjacent tracts of ocean may be almost desti- 
tute of pteropods. I was much surprised in opening the stomach of a large 
sunfish taken off Point Reyes, California, to find it crammed with Cleodora. That 
such a slow and clumsy creature as Orthagoriscus mola could gorge itself with 
the nimble pteropods was indeed remarkable. Another fact of interest was 
developed by the examination of molluscan fragments found in the stomachs of 
the Pacific salmon fresh from the sea, sent me by Professor Kofoid of the Uni- 
versity of California for identification. "These consisted almost exclusively of 
Spirialis and Limacina, showing that the last meal of the fish had been taken in 
cold water. In the Northeast Pacific I have not taken these two genera in the 
open sea, but only near shore in the colder coast currents. 
The form collected by me in 1865 and 1871, and from «nie. | specimens of 
which carefully enlarged colored figures were drawn, differed so much from the 
figures given by Rang, Souleyet, and other authors as representing the Mediter- 
ranean tridentata (= telemus) that it seemed impossible that both should belong 
