38 R. NORRIS WOLFENDEN. 



HETERORRHABDUS (GIESBRECHT). 



Only one specimen of this genus occurs in the ' Discovery ' collection, which is 

 only what might be expected from the fact that the collection is practically only 

 epiplanktonic, whereas Heterorrhabdus is without doubt one of the most confirmed deep- 

 water genera of Copepoda. The species H. austrina (Giesbrecht), which occurs in the 

 ' Belgica ' and ' Gauss ' collections, is absent from those of the ' Discovery,' and the only 

 specimen of the genus occurring in the latter is, I think, referable to H. longicornis. 



HETERORRHABDUS LONGICORNIS. 



Heterochceta lonyicornis, Giesbrecht. Atti. Ace. Line. Rend., Ser. 4, v. (1889) p. 811. 



Fauna u. Fl. Neap. XIX. (1892), p. 373. 



Wolfenden. Jour. Mar. Biol. Assoc., Vol. VII. (1904) p. 124. 

 ? Heterochceta major, Dahl. Verb. d. Zool. (resells., 1894, p. 79. 

 Heterorhabdus major, Wolfenden. Plankton Studies, Part I. (1905), p. 11. 



I first described the male of H. longicornis, hitherto unknown, in 1902. Since 

 then I have found it frequently throughout the Atlantic, extending to the Antarctic 

 area. Dahl's description of II. major is very scanty, and the only essential point of 

 difference between it and longicornis appears to be one of size. The specimen in the 

 'Discovery' collection is a of 4' 5 mm. length, but there is no essential difference 

 between it and smaller males from the Faroe Channel. I suggest therefore that Dahl's 

 H. major is really H. longicornis, and I now think that the species which I described in 

 " Plankton Studies " as //. major may best be described as H. longicornis (Giesbrecht). 



The diagnostic points of H. major (Dahl) are, according to this author, " anterior 

 antennae very long, the posterior foot-jaw with only weak median bristles ; the 

 penultimate lobe of the anterior foot-jaw a long ' tap ' lobe, the mandible teeth but 

 little differing in thickness, nearly the same distance apart ; the exopodite of the third 

 feet like those of the second and fourth, the size over 5 mm. long." 



Except as to size, it will be observed that none of these points differ from those of 

 //. longicornis, the largest examples of which are not, however, more than 3 5 mm. long 

 in the North Atlantic. 



The ' Discovery ' specimen is a $ of 4 5 mm. length, the anterior antennae several 

 joints (about six) longer than the whole body ; the geniculating antennae with six 

 joints beyond the elbow. The right furcal segment is much longer than the left. The 

 fifth lobe of the anterior foot-jaw has a very thick-based stout curved hook, without 

 teeth or bristles except for a few bristles at the proximal end ; the lobe itself is very 

 large. The two other bristles are long and thin. The sixth lobe has a long and thin 

 hook, also uncombed. The bristles of Ri are extremely long. The posterior foot-jaw 

 has a long thin second basal, three times as long as broad, and only two weak bristles 

 in the middle. The mandible has a large simple conical tooth on the outside, and 



