86 



Genus Heteramalla G. O. Sars, 1907(0). 



The characteristic differences between Heteramalla and the other members of the family 

 are: (1) A strong chitinised and slightly bifurcate lamelliform rostrum; (2) An extraordinary deve- 

 lopment of two of the sensory appendages on the apex of the first pair of maxillipedes; and 

 (3) A two-jointed exopodite of the first pair of swimming feet. The exopodites and endopodites 

 of the second, third and fourth pairs of feet resemble those of Xanthocalanus. The fifth pair is 

 very small and rudimentary in the female. The fifth pair of feet of the male is almost similar 

 to that of the male of Scapkoealanus magnus. 



This genus was established by Sars in 1907 for a female Calanoid, apparently identical 

 with a male form from the Gulf of Guinea, described by my father as Amallophora dubia. 



One species is known. It was represented in the 'Siboga' plankton. 



1. Heteramalla dubia (T. Scott). Plate XXXIII, figs. 1 — 9. 



Amallophora dubia T. Scott, 1893, p. 55, pi. IV, figs. 10 — 18. 

 Scolecithrix scotti Giesbrecht, 1897, p. 254. 

 Scolecithrix scotti Giesbrecht & Schmeil, 1898, p. 46. 

 Heteramalla dubia Sars, 1907 (a), p. 17. 



Female — length 3,78 mm. 



Yiewed from above, the body appears moderately robust and oval in outline. The head 

 is distinctly separated from the first thoracic segment. The fourth and fifth thoracic segments 

 are indistinctly divided. The last thoracic segment is slightly produced and appears pointed. 

 Seen from the side, the forehead is feebly arched, and is produced into a very stout, short, 

 chitinised rostrum, bifurcate at the apex and without filaments. The last thoracic segment is 

 narrowly rounded at the apex and, then slightly emarginate as it passes into the dorsal line. 



The abdomen is composed of four segments. The combined length of the abdomen and 

 furca is contained two and three-fourth times in the total length of the ccphalothorax, from 

 the frontal margin to the base of the genital segment. The genital segment is equal to the 

 combined length of the next two segments. The second, third and fourth segments are each 

 shorter than the segment immediately in front. The furcal joints are about as long as broad, 

 and are as long as the anal segment. 



The antennules are twenty-four-jointed and extend to the end of the genital segment. 



The exopodite and the endopodite of the antennae are comparatively short. The endopodite 

 is only slightly shorter than the exopodite. 



The mandibles and maxillae are almost similar to those of Xanthoealanus. 



The apical lobes of the first pair of maxillipedes are furnished with flattened plumose 

 setae. The apex of the first pair of maxillipedes carries three types of sensory organs. The 

 first type is represented by three long and simple appendages which terminate in a blunt point. 

 The second type also consists of three appendages, subequal in length, but each one terminates 

 in a small amalliform head. One of the second series is distinctly stouter than the others and 

 the head is more expanded. The third type is represented by two very short and stout appendages, 

 each with an enormously developed amalla, resembling the single one in Amallophora typica. 



86 



