COPEPODA 37 



Scott suggest that Heterocalanus 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 hasp. 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 princeps 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 



Bathycalanus 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 conies. Pes I has i Se in Re I II, 2 Se in Re III 



Macrocalanus (Bradycalanus) typtciis Scott. 



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

 6. Re pes I with 3 segments. Rostral processes long stiff rounded Bathycalanus maxinms Wolf. 



3. Macrocalanus princeps Brady. 

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



1883. Calanus princeps n. sp. Brady, pp. 36 37, pi. IV ' 1906 ? Heterocalanus medius n. sp. Wolfenden pp. 27 28. 



figs. 3-7. pi. VIII figs. 1-5. 



19041160. Megacalanus princeps n. sp. Wolfenden pp. 112 113. 1908. Megacalanus princeps Brady. Farran p. 21. 



1905. Macrocalanus princeps Brady. G. O. Sars p. 7. 1911 nee. Megacalanus princeps Wolf. Wolfenden pp. 196 198. 



1905 nee. Megacalanus princeps Brady. Wolfenden pp. 35 I 1911? Heterocalanus medius Wolf. Wolfenden pp. 201 202 



pi. I figs. 79. 



1906. Megacalanus princeps Brady. Pearson p. 6. 



taf. XL figs. 15. 



Description f$. Size. Anterior division 5-5 -{-5 mm; posterior 3mm; 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. yb), 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 antennulae 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 



