NO. 6.] ACCOUNT OF THE SPECIES. 85 



somewhat asymmetrical, the left ramus being larger than the right, though 

 the difference is not so pronounced as in the above-mentioned species. The 

 middle apical seta of the left ramus seems in this species also to have been 

 much prolonged; but its exact length cannot be determined, as in all the 

 specimens examined its distal part was broken off. 



The anterior antennae (fig. 5) are not nearly so slender and elongated as 

 in H. norvegica, scarcely exceeding in length the anterior division (conf. 

 figs. 1 & 2), and they are composed of only 24 articulations. 



The posterior antennae (fig. 6). on the whole, agree in their structure 

 with those in H. norvegica, though being somewhat more strongly built. 

 The outer ramus is shorter than the inner, about equalling in length the 

 proximal joint of the latter, and it is divided into 7 well-defined joints, 4 short 

 articulations occurring between the 2nd and last joint. All the joints, except 

 the 1st, carry strong plumose setae. 



The anterior lip (tig. 7) is rather prominent and distinctly trilobate at the 

 end, the lateral lobes being densely ciliated at the edges. The posterior lip 

 (fig. 8) exhibits the usual appearance, and consists of 2 diverging rounded 

 lobes finely ciliated on the edges. 



The mandibles (fig. 9), as in the other species of this genus, have the 

 masticatory part peculiarly modified, with only 3 unusually slender cutting 

 teeth. Of these the outermost is very large, claw-shaped, and provided out- 

 side with a thin lamellar expansion. The other 2 are placed close together, 

 and are separated from the first by a wide semilunar emargination. They 

 differ slightly in the two mandibles, both on the right being bidentate at the 

 tip, whereas on the left (fig. 9 a), only the inner is bidentate, the outer 

 being simple. On both mandibles a ciliated bristle is attached inside the 

 cutting teeth. The palp is normally developed, and has the outer ramus 

 considerably larger than the inner. 



The maxillae (fig. 10) in the present genus are rather unlike those in the 

 typical Calanoids, chiefly on account of the peculiar development of their 

 outer part or palp. In the present species, they agree rather closely in 

 structure with those in H. norvegica, as also with those in the type species 

 H. spinifrons. The masticatory lobe is rather prominent, and the spines 

 clothing its transversely truncated end are unusually slender and densely 

 crowded together. The vibratory plate is comparatively small, and provided 



