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joint of the basiopodite of the second, third, and fourth pairs of swimming feet is not enlarged, 

 and the surface of the endopodites of these feet is furnished with tine spines. The fifth pair of 

 feet of the female is rudimentary. 



A single specimen, unfortunately a male, but apparently possessing some of these characters, 

 was found in one of the plankton collections taken by the 'Siboga', and is described below. 



Only one representative of the genus was obtained. 



i. Monacilla dubia nov. sp. Plate III, figs. 17 — 29. 



Male — Iength 2,3 mm. 



The cephalothorax is oblong ovate in dorsal view. It is considerably contracted in front, 

 and is produced into a small knob. The head is separated from the first thoracic segment by 

 a well defined suture. The fourth and fifth thoracic segments are fused together. The lateral 

 margins of the last thoracic segment are rounded, and are very slightly produced posteriorly. 

 The rostrum consists of two small blunt points. 



The abdomen is composed of five segments, and is nearly equal to two-fifths of the Iength 

 of the cephalothorax. The first four segments are of about equal Iength. The fifth segment is 

 very small, and only about one-third of the Iength of the fourth segment. The furcal joints are 

 rather longer than broad, and are about twice the Iength of the anal segment. 



The antennules are composed of twenty joints, and reach to the end of the fourth 

 abdominal segment. The eighth joint of the right antennule represents four fusecl joints, and 

 the same joint of the left side represents five joints. 



The antennae, mandibles and mandible palps, resemble those of Oxycalanus semispinus. 



The maxillae and first pair of maxillipedes are also similar to those of Oxycalanus semispinus, 

 with the exception, that the maxillae are somewhat rudimentary, and the claw lobe is absent. 



The second pair of maxillipedes have long and slender second and third joints. The last 

 three joints are very small. 



The first four pairs of swimming feet are similar in structure to those of Oxycalanus 

 semispinus, except in the following particulars : — There is no marginal spine on the first joint 

 of the exopodite of the first pair of feet. There are no fine spines on the surface of the third 

 and fourth joints of the exopodite of the second pair of feet. The exopodites, and endopodites, 

 of the third and fourth pairs of feet, are furnished with surface spines as in Oxycalanus semi- 

 spinus, but the method of arrangement is slightly different. The last joint of the exopodite of 

 the fourth pair of feet has only two rows of spines. The first and second joints of the basiopodite 

 of the fourth pair of feet are not furnished with acicular spines. 



The fifth pair of feet is well developed. Each foot consists of a two-jointed basiopodite, 

 and three free joints. The last free joint of each foot, is furnished at the apex with a moderately 

 long curved spine. The right foot has a small rudimentary endopodite. The inner distal angle 

 of the second joint of the basiopodite of the left foot, bears a long spine with a moderately stout 

 base. The whole of the inner margin of the second free joint, and part of the inner margin 

 of the third joint, is furnished with fine spines. 



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