I 2 



Megacalanus, but it is doubtful if they are justified in doing so, as Brady makes no reference 

 to die remarkable hook on the second joint of the basiopodite of the first feet, vvhich is a 

 pronounced character in Megacalanus. It is very unlikely that Brady would overlook this hook, 

 had it been present in his Calanus ftrinceps, as he notes the occurrence of a hook in Calanus 

 gracilis which is a much smaller form. The hook is quite as pronounced as in Wolfenden's 

 type of the genus Megacalanus. I regard Brady's Calanus princeps to be a member of a new 

 genus mentioned later. On the other hand I include under the genus Megacalanus two species 

 hitherto regarded as true Calanus. They are of much smaller size than the type of the genus, 

 and have only two marginal spines on the last joint of the exopodites of the second, third, and 

 fourth feet. They have, however, the strong hook on the anterior surface of the second joint 

 of the basiopodite of the first feet. This hook is quite distinct from that found in Canthocalanus. 

 In Megacalanus the hook is a well defined projection from the surface of the joint, and has 

 a plumose seta articulated to it. In Canthocalanus the seta is transformed into a strong spine 

 with a hooked base. Three members of this genus were represented in the Siboga plankton. 



Remarks. I include under the genus Megacalanus only those Calanoids that have the 

 anterior surface of the second joint of the basiopodite of the first pair of feet furnished with 

 a strong hook as originally defined by Wolfenden. I do not think that size alone should have 

 any generic or specific importance, so long as the principal character established in the original 

 definition is upheld. 



i. Megacalanus gracilis (Dana). 



Calanus gracilis Dana, 1849, pp. 18, 24. 



Calanus gracilis Brady, 1883, p. 35, pis. V & XLVI. 



Calanus gracilis I. C. Thompson, 1888, p. 147. 



Calanus gracilis Giesbrecht, 1893, p. 90, pis. I, 6, 7, 8. 



Calanus gracilis T. Scott, 1893, p. 25. 



Calanus gracilis Giesbrecht, 1895, p. 248. 



Calanus gracilis Giesbrecht & Schmeil, 189S, p. 17. 



Calanus gracilis I. C. Thompson, 1900, p. 275. 



Calanus gracilis I. C. Thompson, 1903, p. 15. 



Calanus gracilis Thompson & Scott, 1903, p. 241. 



Calanus gracilis Cleve, 1903, p. 357. 



Calanus gracilis Sars, 1905 (a), p. 1. 



Calanus gracilis Esterly, 1905, p. 128, fig. 4. 



Calanus gracilis Pearson, 1906, p. 5. 



Calanus gracilis Farran, 1908, p. 20. 



Calanus gracilis van Breemen, 1908, p. 10, fig. 7. 



Megacalanus gracilis although generally distributed over the area investigated, appeared 

 to be rather scarce in numbers. It was noted at the following stations. 



Stat. 19. — Stat. 35. — Stat. 40. — Stat. 66. — Stat. 75. — Stat. 89. — Stat. 98. — 

 Stat. 99. — Stat. 110. — Stat. 1 1/\ — Stat. 118. — Stat. 125. — Stat. 125 (night) — 

 Stat. 12S. — Stat. 129. — Stat. 133. — Stat. 141. — Stat. 143. — Stat. 148. — Stat. 157. — 

 Stat. 177". — Stat. 189*. — Stats. 194 — 7. — Stat. 203 (1500 metres). — Stat. 204. — 

 Stat. 220 (vertical net). — Stat. 220 (surface). — Stat. 243. — Stat. 245. — Stat. 252. — 

 Stat. 276. — Stat. 282. 



