32 



two free joints attached to the basal portion. In the male, the left foot is greatly elongated, 



and is composed of five joints. The right foot is very short and consists of one or three joints. 



Two species belonging to this genus were represented in the 'Siboga' plankton. 



i . Clausocalanus arcuicornis (Dana). 



Calanus arcuicornis Dana, 1849, P- I2> 



Claitsocalamts arcuicornis Giesbrecht, 1893, p. 186, pis. I, 2, 10, 36. 



Clausocalanus arcuicornis T. Scott, 1893, p. 73, pi. 8. 



Clausocalanus arcuicornis Giesbrecht & Schmeil, 1898, p. 27. 



Clausocalanus arcuicornis I. C. Thompson, 1900, p. 277. 



Clausocalanus arcuicornis Wheeler, 1900, p. 171, fig. 9. 



Clausocalanus arcuicornis Cleve, 1901, p. 5. 



Clausocalanus arcuicornis Thompson & Scott, 1903, p. 243. 



Clausocalanus arcuicornis Farran, 1903, p. 1 1. 



Clausocalanus arcuicornis Cleve, 1903, p. 359. 



Clausocalanus arcuicornis Cleve, 1904, p. 188. 



Clausocalanus arcuicornis Esterly, 1905, p. 142, fig. 13. 



Clausocalanus arcuicornis Sars, 1905 («), p. 3. 



Clausocalanus arcuicornis Wolfenden, 1905 (a), p. 999. 



Clausocalanus arcuicornis Pearson, 1906, p. 9. 



Clausocalanus arcuicornis Farran, 1908, p. 28. 



Clausocalanus arcuicornis van Breemen, 1908, p. 23, fig. 20. 



This species was moderately common, and appeared to be generally distributed in the 

 area investigated, as shewn by the following records. 



Stat. 16. — Stat. 19. - - Stat. 35. — Stat. 36. — Stat. 47 1 '. — Stat. 71. — Stat. 75. — 

 Stat. 93. — Stat. 96 (day). — Stat. 96 (night). -- Stat. 98. -- Stat. 112. -- Stat. 118. — 

 Stat. 121. -- Stat. 128. — Stat. 141. — Stat. 142. — Stat. 143. — Stat. 148. — Stat. 168. — 

 Stat. 174. — Stat. 185. -- Stat. 203 (1500 metres to surface). — Stat. 205. — Stat. 213. — 

 Stat. 215'. - - Stat. 217 (horizontal cylinder). — Stat. 220 (vertical net). -- Stat. 223. — 

 Stat. 224. -- Stat. 225. -- Stat. 230. — Stat. 243. -- Stat. 276. — Stat. 282. — Stat. 315. 



The females of Clausocalanus arcuicornis, are not unlike those of the next species. They 

 are rather larger than Clausocalanus furcatus, and can be separated by the difference in the 

 lengths of the segments of the abdomen and furcal joints. In this species the genital segment 

 is longer than each of the next two segments. The furcal joints are about as long as broad. 



This species has a wide distribution in the warm seas. It has also been recorded from 

 the deep water of the Atlantic, off the West Coast of Ireland by G. P. Farran. 



2. Clausocalamis furcatus (Brady). 



Drcpanopus furcatus Brady, 1883, p. "/j, pis. IV & XXIV. 

 Clausocalanus furcatus Giesbrecht, 1893, p. 186, pi. 36. 

 Clausocalanus furcatus T. Scott, 1893, p. 72. 

 Clausocalanus furcatus Giesbrecht, 1896, p. 318. 

 Clausocalanus furcatus Giesbrecht & Schmeil, 1S98, p. 27. 

 Clausocalanus furcatus Cleve, 1901, p. 5. 

 Clausocalanus furcatus A. Scott, 1902, p. 403. 

 Clausocalanus furcatus Thompson & Scott, 1903, p. 244. 



