42 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



mens the posterior body is usually bent back at right angles to the 

 anterior body, as noted by Scott and Pesta. 



Family PSEUDOCALANIDAE 



Genus CLAUSOCALANUS Giesbrecht, 1888 



Head fused with the first segment; fourth and fifth segments also 

 fused, with rounded posterior corners ; urosome 4-segmented ; exopod 

 of second antenna 6-segmented, longer than the endopod; first an- 

 tennae just reaching the genital segment; exopods of the first four 



pairs of legs 3-segmented; 

 first endopod 1-segmented, 

 second endopod 2-segmented, 

 third and fourth endopods 

 3-segmented; fifth legs uni- 

 ramose, 3-segmented ; basi- 

 pods and exopods of second 

 and third legs considerably 

 wider than those of the 

 fourth legs. One species. 



CLAUSOCALANUS ARCUICORNIS 

 (Dana) 



FiGtJBB 24 



Calanus arouicornis Dana, Proc. 

 Amer. Acad. Arts and Sci., 

 vol. 2, p. 12, 1849. 



Claiisocalantis arcuicornis Gies- 

 brecht and ScHMErL, Das 

 Tierreich, Lief. 6, Copepoda 

 p. 27, 1898. 



Occurrence. — Three males 

 and numerous females were 



'Clausocalanus arcuicornis: a. Female, taken by Wheeler at the SUr- 

 b, male, dorsal; c, fifth legs, male; f^ce in the Gulf Stream 



south of Marthas Vineyard. 



Distribution. — ^Messina (Glaus) ; Mediterranean, tropical Atlantic 

 and Pacific (Giesbrecht) ; Indian Ocean, Ked Sea (Thompson and 

 Scott) ; northern Atlantic (Cleve) ; Arabian Sea, Indian Ocean, 

 Malay Archipelago (Cleve). 



Color. — Not very transparent, with red pigment in some parts of 

 the thoracic segments, on the dorsal and ventral surfaces, and in the 

 genital segment. In the male the pigment is on the whole more 

 abundant and may extend into the basal segments of the first anten- 

 nae. In rare instances all the cuticle has a violet color ; the eggs are 

 rose colored (Wheeler). 



Figure 24.- 

 dorsal 

 d, fifth legs, female. 



