developed, with the normal number of setae, Anterior antennae composed of a 

 limited number of well defined joints, and extended laterally. No traces 

 of posterior antennae and oral appendages observable, nor of any distinct oral 

 tubule. Three pairs only of natatory legs present, the 2 posterior pairs of legs 

 being quite rudimentary and of similar structure. Two ovisacs present in female. 

 Remarks. In the above diagnosis i have attempted to give the most 

 essential characters, by which the present genus distinguishes itself from the 

 other known Monstrilloida. The mutual relation of the 2 chief divisions of 

 the body is very peculiar, and does not agree either with that mentioned by 

 Giesbrecht as characteristic to his suborder Gymnoplea or with that characterising 

 the Podoplea, the movable articulation between the 2 divisions occuring in 

 quite a different place, viz., at the junction between the penultimate and anti- 

 penultimate trunk-segments. This is indeed a quite unique character distinguishing 

 this genus from any other form known to me. As anomalous characters may also 

 here be named the presence of only 3 pairs of natatory legs, and the narrow 

 rod-like shape of the last caudal segment. The genus comprises as yet only 

 a single species, to be described below. 



1. Thaumatopsyllus paradoxus, G. O. Sars. 



(Pi. i.) 



I haiima topsylltis paradoxiis, O. O. Sars, Arch. f. Mathcni. og Naturvidenskab. Bd. XXXIII. 



No. 6, p. 5, w. plate. 



Specific Characters. Female. Body comparatively slender, with the 

 anterior division somewhat depressed and oblong oval in outline. Cephalic seg- 

 ment very large and slightly contracted anteriorly, frontal part narrowly rounded. 

 The 2 succeding segments well developed, with the lateral parts closely conti- 

 guous and rounded behind. Penultimate trunk-segment scarcely more than 

 half as broad as the preceding one; last segment still smaller. Tail exceedingly 

 slender, almost attaining half the length of the body; genital segment slightly 

 constricted in the middle; 2nd segment quite short and having the posterior 

 edge somewhat produced dorsally; 3rd segment more than twice as long a> 

 the other 2 combined, and extremely narrow, rod-like, with the slightly dilated 

 extremity transversely truncated. Caudal rami but slightly diverging and oblong 

 quadrangular in form, being about 4 times as long as they are broad, and 

 a little widening distally; seta of outer edge occuring about in the middle; 

 apical setae of moderate size and densely ciliated, the outermost one shorter 

 than the other 3. Antennae not nearly attaining the length of the cephalic 



