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As our knowledge of this peculiar group of Isopoda is of comparatively recent 

 date, it is highly probable, that the number of genera will, in course of time, be 

 considerably increased, and that it will even be found necessary to subdivide 

 this group into several distinct families. 



Gen. 1. MunnOpSlS, M. Sars, 1860. 



Generic Characters. — Body less compact than in the other genera, with 

 the anterior division much broader than the posterior. Cephalon of moderate 

 size, deeply emarginated on each side for the insertion of the antenna?, frontal 

 part narrowly produced. The 4 anterior segments of mesosome transversely ex- 

 cavated dorsally, with the lateral parts obtuse; the 3 posterior segments densely 

 crowded together, and very convex above. Caudal segment comparatively large, 

 oblong oval. Superior antennas with the basal joint very large and massive, flagellum 

 niultiarticulate and much longer in male than in female. Inferior antenna? with 

 the 2 outer joints of the peduncle greatly elongated. Mandibles without any 

 molar expansion, cutting edge but slightly dentated, palp well developed, with the 

 terminal joint lamellar, incurved. Maxillipeds pronouncedly laminar, with the 

 antepenultimate joint of the palp acutely produced inside, the 2 outer joints 

 narrow and simple. The first 2 pairs of legs of essentially the same structure, though 

 somewhat different in size; the 2 succeeding pairs extremely slender and elong- 

 ated, with the first 3 joints short and thick. Natatory legs of uniform structure, 

 and rather slender, with the carpal and propodal joints foliaceous and densely 

 edged with plumose seta?, dactylus wanting. Female operculum navicular, male 

 operculum transformed in the usual manner, digitiform process of the copulative 

 appendages terminating in a long and slender seta. Uropoda simple, filiform, 

 biarticulate. 



Remarks. — This genus was established in the year 1860 by my late father, 

 to include a very remarkable Isopod, found by him at Christiansund, west coast of 

 Norway. The generic name refers to a certain resemblance, in outward appear- 

 ance, to the genus Munna of Kroyer. It forms the type of the family Munnop- 

 sidw, being the first genus recorded, and it is distinguished pretty well from the 

 other genera, both by its outward appearance, and by the structure of the several 

 appendages. In addition to the type species, 4 other species have in recent times 

 been adduced to this genus. Three of these were procured during the Challenger 



