very like Acrocalaiuis longicornis in general appearance, is readily separated by its smaller 

 size, and shorter antennules. 



This Acrocalanus has a distribution similar to that of the two previous species. 



4. Acrocalanus monachus Giesbrecht. 



Acrocalanus monachus Giesbrecht, 1888, p. 333. 

 Acrocalanus monachus Giesbrecht, 1S93, p. 171, pis. 6 & 10. 

 Acrocalanus monachus Giesbrecht & Schmeil, 1898, p. 25. 

 Acrocalanus monachus Thompson & Scott, 1903, p. 243. 

 Acrocalanus monachus Cleve, 1903, p. 356. 

 Acrocalanus monachus Wolfenden, 1905 (a), p. 1002. 



This appeared to be the least common species of the genus, and was only noted at 

 the following stations. 



Stat. 98. — Stat. 99. — Stat. 128. — Stat. 217. 



Acrocalanus monachus has a very characteristic head when seen in lateral view, which 

 makes the identification comparatively easy. The forehead when seen from the side, is mode- 

 rately broad and nearly truncate in outline. 



This species up to the present, has been recorded only from the Pacific and Indian 

 Oceans, and from the Red Sea. 



Genus Calocalanus Giesbrecht, 1888. 



The members of this genus are not unlike Paracalanus, but are easily recognised by 

 the abdomen being composed of only two or three joints, by the long terminal joint of the 

 antennules, and by the structure of the fifth feet. The fifth feet of the female are symmetrical, 

 and consist of two or three free joints attached to a basal portion. The right foot of the 

 male is composed of three free joints, and the left foot of five. The left fifth foot is conside- 

 rably elongated, and is slightly prehensile. 



Two species were obtained from the 'Siboga' plankton. 



1. Calocalamis pavo (Dana). 



Calanus pavo Dana, 1S49, p. 13. 



Calocalanus pavo Giesbrecht, 1893, p. 175, pis. 1, 4, 9, 36. 



Calocalanus pavo T. Scott, 1893, p. 37, pi. 6, figs. 9 & 10. 



Calocalanus pavo Giesbrecht, 1896, p. 31S. 



Calocalanus pavo Giesbrecht & Schmeil, 1898, p. 26. 



Calocalanus pavo I. C. Thompson, 1900, p. 277. 



Calocalanus pavo Wheeler, 1900, p. 169, fig. 7. 



Calocalanus pavo Cleve, 1901, p. 5. 



Calocalanus pavo A. Scott, 1902, p. 402. 



Calocalanus pavo Thompson & Scott, 1903, p. 243. 



Calocalanus pavo Cleve, 1903, p. 357. 



Calocalanus pavo Cleve, 1904, p. 186. 



Calocalanus pavo Wolfenden, 1904, p. III. 



3° 



