20 PROCEEDINGS OF THE NATIONAL MUSEUM vol.80 



the year on the mackerel-fishing grounds of Ireland, but as becoming 

 more numerous in autumn. He also said that longiremis was not 

 found there at all, and hence did not share \Yith clausii in furnishing 



food. 



In a continuous collection of plankton from Liverpool to Quebec, 

 made by W. A. Herdman in 1897, these two Acartia species were 

 taken along the English and American shores but disappeared en- 

 tirely in the open ocean. Hence they may be regarded as littoral 

 rather than pelagic species, well suited to such a region as Chesa- 

 peake Bay. 



ACARTIA LONGIREMIS (Lilljeborg) 



Diaa longiremis Lilljeborg, De Ciustaceis ox ordinibus tribus in Scania 



occurrentibus, p. 181, pi. 24, 1853. 

 Acartia longiremis G. O. Sabs, Crustacea of Norway, vol. 4, p. 149, pis. 99, 



100, 1903. 



Occurrence. — Taken at every station in the bay, in the surface, the 

 bottom, and the vertical nets ; most abundant in March. 



Remarks. — Sars, in the reference given above (p. 150), said of 

 this species : " It is a true pelagic form, being often met with far 

 out at sea, and at the very surface. Not unfrequently, however, it 

 is brought by the current close to shore ; and it is even often found 

 in tidal pools together with Paracalanus farous and Tetnora longi- 

 cornis.''^ Its abundant distribution in Chesapeake Bay shows also 

 that it may become essentially a littoral form. Its presence there 

 is not dependent upon currents or tide pools ; it is indigenous to the 

 bay and forms one of the two chief constituents of the copepod 

 plankton. Furthermore, it is just as abundant in the brackish water 

 of the inner bay as in the outer bay, the salinity of which is nearly 

 as high as that of the ocean. 



This species occupies a position next to A. clausii and shares with 

 the latter its economic importance as a component of the plankton 

 food supply. Though its proportion to clausii is usually that of the 

 2 : 8 ratio already mentioned, it frequently falls to 20, 10, or even 5 

 per cent. Usually, however, it maintains a good average, and rarely 

 it exceeds the former species in numbers. 



AMALLOPHORA BREVICORNIS G. O. Sars 



Scolecithriw brevicornis G. O. Sars, The Norwegian North Polar Expedition, 



Crustacea, p. 46, pi. 10, 1900. 

 Amallophora hrevicornis G. O. Sars, Crustacea of Norway, vol, 4, p. 53, pi. 



36, 1902. 



Occurrence. — Obtained only in the bottom net at the 100-fathom 

 line in the ocean outside the bay. 



Remarks. — A pelagic form not likely to be found in the bay but 

 not before reported from American shores. 



