

CYCLOPOIDEA. HQ3 



Genus HEMICALANUS, Dana. 



Rostrum infra furcatum. Oculi duo simplices tantum,pigmentis scepis- 

 sime coalitis, minutis. Antennae anticce maris parce impares, dextrd 

 cum articulatione genicidante, articulis raro coalitis. Antennas posticce 

 biremes, ramis subcequis ; ramo laterali 2-articulato, articulis duobus 

 suboBquis, apice 3 setas gerente et a,rticuli primi dorso setigero. Maxil- 

 lipedes recti, grandes, elongate setigeri. Pedes postici maris impares, 

 dextro crasse prehensili ; feminae sive precedentibus similes sive parvuli. 



Beak furcate below. Eyes two, simple, the pigment of the two usually 

 united, minute. Anterior antennas of male sparingly dissimilar, the 

 right having a geniculating joint, the joints in few cases coalescing. 

 Posterior antennas two-branched, the branches subequal, lateral 

 branch often the longer, two-jointed, joints subequal, at apex of this 

 branch three setae, and several on the back margin of the first joint. 

 Posterior feet in males dissimilar, the right stout prehensile; in 

 females, either like the preceding, or obsolescent. 



This genus, like Undina, is intermediate between Pontella and 

 Calanus. It has the posterior antennae of Calanus and Undina, and 

 the anterior antennae have a Calanoid position, the tips being behind 

 or but little in advance of the beak. Moreover, the inferior eyes of the 

 Pontellae are wanting. But like the genus Pontella, the right male 

 antenna has a geniculating joint, yet with but little modification of 

 the organ, and also, the posterior thoracic legs are dissimilar, and one 

 is large prehensile ; besides, the maxillipeds are larger if not longer 

 than the anterior feet, and the setae extend forward beneath the 

 mouth, as particularly described under Pontella. The genus Undina 

 differs from this in having no geniculating joint in the male antennae, 

 these organs on both sides having instead a slight bend, one-third of 

 the way from the base. Diaptomus of West wood (including the C. 

 castor, a fresh-water species) differs from Hemicalanus in having the 

 posterior thoracic legs in the female quite large and stout, and the 

 shorter branch of the posterior antennae with several short joints at 

 middle. As no species of Hemicalanus or of Pontella has been ob- 



