2 9 



of its antennules. The antennules extend beyond the body by five joints. It can be also 

 recognised by the armature of the distal part of the last joint of the exopodites of the fourth 

 pair of feet. The armature consists of a number of very fine teeth. 



This species has been recorded from the Atlantic, Indian, and Pacific Oceans, and also 

 from the Red Sea. 



2. Acrocalanus gracilis Giesbrecht. 



Acrocalanus gracilis Giesbrecht, 1888, p. 332. 

 Acrocalanus gracilis Giesbrecht, 1893, p. 171, pis. 6 & 10. 

 Acrocalanus gracilis Giesbrecht, 1897, p. 318. 

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

 Acrocalanus gracilis Cleve, 1901, p. 4. 

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

 Acrocalanus gracilis Cleve, 1903, p. 356. 

 Acrocalanus gracilis Cleve, 1904, p. 184. 

 Acrocalanus gracilis Wolfenden, 1905 (a), p. 1003. 



This Acrocalanus although not so common as the preceeding species, was more plentiful 

 than either of the next two. It occurred at the following stations. 



Stat. 16. — Stat. 36. — Stat. 40. — Stat. 75. — Stat. 93. — Stat. 98. — Stat. 99. - 

 Stat. 101. - - Stat. 109. — Stat. 117». - - Stat. 118. — Stat. 138. -- Stat. 141. -- Stat. 



142. — Stat. 143. — Stat. 148. — Stat. 203 (1500 metres to surface). - - Stat. 213. - 

 Stat. 2 1 5 a . — Stat. 2XJ (horizontal cylinder). — Stat. 224. — Stat. 225. — Stat. 229. - 

 Stat. 243. — Stat. 245. — Stat. 315. 



This species is easily distinguished from the other three, by its larger size, and by the 

 smoothly rounded dorsal surface of the cephalothorax, when viewed from the side. 

 Acrocalanus gracilis has a distribution similar to the preceeding species. 



3. Acrocalanus gibber Giesbrecht. 



Acrocalanus gibber Giesbrecht, 1888, p. 332. 

 Acrocalanus gibber Giesbrecht, 1893, p. 171, pis. 6 & 10. 

 Acrocalanus gibber Giesbrecht & Schmeil, 1898, p. 65. 

 Acrocalanus gibber I. C. Thompson, 1900, p. 276. 

 Acrocalanus gibber Cleve, 1901, p. 4. 

 Acrocalanus gibber A. Scott, 1902, p. 402. 

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

 Acrocalanus gibber Cleve, 1903, p. 356. 

 Acrocalanus gibber Cleve, 1904, p. 184. 

 Acrocalanus gibber Wolfenden, 1905 («), p. 1003. 



Acrocalanus gibber although not common, apparently had a moderately wide distribution 

 in the area traversed by the 'Siboga', as shewn by the following records. 



Stat. 16. — Stat. 19. - - Stat. 35. - - Stat. t,6. — Stat. ^-j. — Stat. 47''. — Stat. 93. — 

 Stat. 98. — Stat. 112. — Stat. 118. — Stat. 138. — Stat. 141. — Stat. 142. — Stat. 



143. — Stat. 184. -- Stat. 2i5 a . — Stat. 217 (horizontal cylinder). — Stat. 315. 



This species when present, can be easily identified by its very compact body, and although 



