COPEPODA 



37 



Scott suggest that Hctcrocalamcs medius Wolf, is identical with Kroyers Calanus cristatus; 

 this species, of which I have examined the type specimens, is however a true Calanus (cf. p. n). 

 On account of the existing confusion I think the following synoptic key will be useful. 



i. Strong hook on anterior surface of basp. Ill pes. i ; pes I — IV with 3 segmented Re and Ri. The 

 maxillae without densely plumous setae in distal lobes Megacalanus 2. 



1. Strong hook on anterior surface of basp. Ill pes I wanting 3. 



2. 3 Se of Re III of pes II — IV Megacalanus princcps Wolf. 



2. 2 Se of Re III of pes II— IV Calanus gracilis Dana. 



Calanus robustior Giesb. 



3. Maxillae without densely plumous setae. 2 Se of Re III of pes II — IV Calanus 



3. Maxillae with densely plumous setae. 3 Se of Re III of pes II — IV 4. 



4. Maxillipeds with slender setae Macrocalanus. 5. 



4. Maxillipeds with densely plumous setae. Re pes I without Se. Front with 2 conical processes 



Bathy calanus G. O. Sars. 6. 



5. Frontal crest. Rounded lateral corner. Pes I has no Se in Re I — II, one Se in Re III 



Macrocalanus (Heterocalanus) princeps Brady. 



5. Frontal crest wanting. Pointed lateral cornes. Pes I has 1 Se in Re I — II, 2 Se in Re III 



Macrocalanus (Bradycalanus) tyficus Scott. 



6. Re pes I two segmented. Rostral processes rather slender Bathy calanus Richardi G. O. Sars. 

 6. Re pes I with 3 segments. Rostral processes long stiff rounded Bat 7iy calanus maximus W olf. 



3. Macrocalanus princeps Brady. 

 (PI. I figs. 2a — b; textfigs. 7a — b). 



1883. Calanus princeps n. sp. Brady, pp. 36 — 37, pi. IV 



figs- 3-7- 



1904 nee. Megacalanus princeps n. sp. Wolfenden pp. 112— 113. 



1905. Macrocalanus princeps Brady. G. O. Sars p. 7. 



1905 nee. Megacalanus princeps Brady. Wolfenden pp. 3—5 



pi. I figs. 7—9. 



1906. Megacalanus princeps Brady. Pearson p. 6. 



1906 ? Heterocalanus medius n. sp. Wolfenden pp. 27 — 28. 



pi. VIII figs. 1-5. 

 1908. Megacalanus princeps Brady. Farran p. 21. 



191 1 nee. Megacalanus princeps Wolf. Wolfenden pp. 196 — 198. 

 1911 ? Heterocalanus medius Wolf. Wolfenden pp. 201 — 202 



taf. XL figs. 1—5. 



Description i% Size. Anterior division 5-5 -[-5 mm; posterior 3 mm; total length 13-5 mm. The 

 body is slender, as the anterior division is about 2-5 as long as wide. The first as well as the fifth somite, 

 the lateral corner of which is regularly rounded (fig. 7 b), are well distinguished. The head has a low 

 crest terminated by a small frontal process. The rostrum consists of two powerful rounded spines, 

 parallel and directed downwards. At the base slender rostal filaments protected above by low pro- 

 cesses. The hinder margin of the head has dorsally a small elevation bearing a conical process. The 

 urosome consists of four somites, of which the first — the genital one — , ventrally produced in front, 

 dorsally behind, is distinctly wider and deeper than long, and distinctly twice as long as the following 

 somites. The furcal rami are a little shorter than the third somite and 1-2 as long as wide. 



The ant ennui a e project at least 6 segments beyond the tip of the furca; they consist of 25 

 segments, of which, however, the 8 and 9 are less well separated. The segments increase in length 



