DEPAETMENT OF MARINE BIOLOGY. 171 



It was remarkable, however, that in the tropical Pacific, whenever we met 

 with a decided counter current running in an easterly direction against the 

 prevailing westerly drift, the water became relatively acid, ranging from 8.1 

 to 8.18 PH. This easterly counter current is often encountered in the mid- 

 Pacific about 5° north of the equator, in the region of such low-lying coral 

 islets as Palmyra, and the Phoenix or Union Groups, and is a menace to 

 vessels because of the absence of hghthouses, the uncertainty of the presence 

 or absence of the current, and the difl&culty in seeing submerged reefs and 

 small low islands at night. 



The ease and rapidity with which anyone can test the alkalinity of sea- 

 water, using some such indicator as thymolsulphonepthalein, may enable 

 this method to become of aid to navigation in these dangerous waters. One 

 has only to mix the water with a few drops of the dye, and if the mixture 

 is greenish-blue it is alkaline, while an approach toward acidity produces 

 a more nearly yellow color. This m.ethod may also be used wherever the 

 ship passes out of a current of tropical origin, which, being warm, is alkaline, 

 into another current of colder water, which, due to its low temperature, is 

 relatively less alkaline than the sea-water of the tropics. 



The presence of CO2 causes the sea-water to become relatively acid, and it 

 is possible that in the mid-Pacific the easterly counter current of relatively 

 acid water may be derived from cold, deep water which, upon rising to the 

 surface, becomes warmed to a temperature practically identical with that of 

 the surrounding westerty set, but still retains some of the CO2 characteristic 

 of the waters of the deep sea. Indeed, one would expect that the general 

 westerly trend of the surface-waters along the wide equatorial belt of the mid- 

 Pacific may set up a counter current in the underlying depths tending to 

 counterbalance the surface drift. Occasionally this deep-lying counter cur- 

 rent may appear upon the surface, in which case it still retains some of its 

 easterly movement and some of its excess of CO2. 



Report of Work done upon Annelids in 1918, hy A. L. Treadwell. 



My work for this season was a continuation of that of previous years, the 

 preparation of a monograph of the Leodicidse of the West Indian region. 

 Having made an exhaustive study of the Tortugas and of the northern Umit 

 of this West Indian region at Bermuda, the research for 1918 was conducted 

 at its southern hmit in Tobago. Most of the collections were made off Pigeon 

 Point, on Buccoo Reef, and in Buccoo Bay. Petit Trou Lagoon yielded the 

 same mud-Hving forms that were found in Buccoo Bay, and one new species 

 of Marphysa was found only on the sandy beach about a mile west of Scar- 

 borough. No Leodicidse could be found at Man O'War Bay, the only anneUds 

 obtained there being a species of a Spionid. 



A considerable number of the Leodicidse occur throughout the West Indian 

 region, the most constant being Nicidion kinhergii Webster, which has appeared 

 in all of my collections and is always abundant in the outer layers of the 

 decomposed coral rock. It is noteworthy that the relative abundance of most 

 of the other species varies in different localities. Thus in Bermuda the com- 

 monest form is Leodice mutilata, in the Tortugas it is Leodice fucata, while in 

 Tobago the large Leodice carihoea was common. L. fucata, the "palolo," has 

 not been described from Bermuda and was rare in Tobago. Evidently its 

 range is in the middle of the West Indian region. No observations were 

 obtained on the question of its swarming. It was hoped to study this phenom- 

 enon in the Bahamas, but war conditions made it impossible to visit that 

 region this year. 



