iBT. 15 COPEPOD CRUSTACEANS OF CHESAPEAKE BAY WILSON 49 



winter. It is also found in the outer bay during autumn and proba- 

 bly during spring and in the inner bay during spring. Cleve, in 

 discussing the geographical distribution of Atlantic Copepoda and 

 their physical conditions,^" gave 20.29 as the mean salinity of the 

 water in which this species was found. In the records here given 

 the average salinity is much less than that, and at several stations 

 was less than 10. This species, therefore, can accommodate itself to 

 marked changes in salinity with almost as much ease as the two 

 species of Acartia and Harpacticus gracilis. 



OITHONA PLUMIFERA Baird 



Oithona plumifera Baird, Newman's Zool., vol. 1, p. 59, 1843. — Giesbrecht, 

 Fauna und Flora des Golfes von Neapel, vol. 19, p. 754 ; pis. 4, 34, 44, 1892. 



Occurrence. — This copepod was not found within the limits of the 

 bay, but many specimens were obtained in the bottom net from 

 depths of 20 and 118 fathoms in the outside ocean. 



Remarks. — This is a pelagic form and not likely to be found within 

 the limits of the bay. It has never been found anywhere in sufficient 

 abundance to become of more than scientific interest. 



OITHONA SIMILIS Clans 



Oithona similis Claus, Die Copepodenfauna von Nizza, p. 14, 1866. — G. O. 

 Saks, Crustacea of Norway, vol. 6, p. 6 (1918, p. 207), pi. 3, 1913. 



Occurrence. — Found at every station in the bay except D, H, M, 

 and U; found much more abundant in the imier bay, but not so 

 well distributed nor in such large numbers as brevicornis; decidedly 

 a winter form but present also at other seasons. 



Remarks. — Fish lists this copepod as a summer form at Woods 

 Hole, and Wheeler obtained his specimens in July. Chesapeake Bay 

 is much farther south, and while this species was found sometimes 

 in summer in the outer bay, it was taken almost exclusively during 

 autumn and winter in the inner bay. Like hrevicomis^ it was pres- 

 ent in sufficient numbers to offset its diminutive size and formed an 

 important addition to the plankton. 



OITHONA SPINIROSTRIS Claus 



Oithona spinirostris Claus, Die frei lebenden Copepoden, p. 105, pi. 11, figs. 

 4-9, 1863.— G. O. Sabs, Crustacea of Norway, vol. 6, p. 6, pis. 1, 2, 1913. 



Occurrence. — A few specimens were taken in a surface net at 

 Station G on December 4, 1920. About 40 specimens were also 

 obtained in a bottom net at a depth of 20 fathoms in the outside 

 ocean during the trip to the 100-fathom line on August 21, 1920. 



^^ Ofversigt af Kongl. Vetenskaps-Akademiens FSrhandllngar, p. 139, 1900. 



