copulative appendage divided at the end into 2 comparatively short diverging 

 lobes. Caudal rami of a similar shape to those in Ihe female, but each 

 provided with 4, instead of 3, setae of nearly equal length. Antennae compara- 

 tively much larger than in female, and each composed of 5 well defined 

 joints, the 3 middle ones lamellarly expanded inside and armed with several 

 short spines in addition to the setae, last joint comparatively small, but very 

 movably articulated to the preceding one. Natatory legs agreeing exactly in 

 structure with those in female. 5th pair of legs wholly absent. 



Body, as usual, much more transparent in female than in male, being 

 in the latter, according to Giesbrecht, everywhere of a dark fuscous colour. 



Length of adult female 2.603.16 mm., of male 2.30 mm. 



Remarks. The present form is chiefly characterised by the extraordinary 

 length of the ovigerous spines in the female and their peculiar coalescence 

 at the base. In its general appearance it bears a very close resemblance to 

 the form recorded by Claparede under the name of Monstrilla dance, and, 

 were it not that no mention has been made by that author on the above- 

 named distinguishing character, I should indeed have been much inclined to 

 regard these 2 forms as identical. 



Occurrence. The present species, it is true, has not yet been observed 

 off the Norwegian coast; but I regard it as very probable that on further 

 investigations it will be found to occur in some place or other on the south 

 and west coast. As I have had an opportunity of examining this form, I 

 find it advisable to give here a detailed description of it, for comparison with 

 the other 2 species. The figures given on PI. XIII have been drawn from 

 specimens collected during one of the Monaco-Expeditions in the Mediterranean 

 off Sardinia. 



Distribution. British Channel (Bourne), Mediterranean at Naples (Gies- 

 brecht). 



Gen. 4. Monstrillopsis, G. O. Sars, n. 



Generic Characters. Body of very different appearance in the 2 sexes, 

 being exceedingly slender in female, much shorter and stouter in male. Tail 

 composed in female of 3 well defined segments, the middle of which is the 

 smallest, in male distinctly 4-articulate. Caudal rami in both sexes of the 

 very same structure, being unusually produced, and each provided with 4 well 



4 Crustacea. 



