11 



guished from the other 2 genera comprised within the present family by the 

 more complete segmentation of the tail and the increased number of caudal 

 setae. Another character by which the species of this genus may be readily 

 recognised, is the position of the oral tubule, wich is more or less far remote 

 from the frontal part of the head, whereas in the other 2 genera it generally 

 occurs in close approximation to that part. 



Seven Norwegian species referable to this genus will be described in the 

 sequel, one of them being, however, somewath doubtful and only observed in 

 the male sex. 



2. Monstrilla longicornis, Thompson. 

 (Pi. II & ill). 



Monstrilla longicornis, I. C. Thompson, Trans. Biol. Soc. Liverpool, Vol IV, p. 119, PI. IV, 



figs. 1, 2, 4 (cf). 

 Syn: Mcnstrilla intermedia, Aurivillius. 



Specific Characters. Female. Body moderately slender, with rather coarse 

 integuments, which exhibit everywhere a finely granular or dotted surface. 

 Cephalic segment occupying about half the length of the body, and almost of 

 equal width throughout, though, seen dorsally, exhibiting somewhat behind the 

 middle a slight but easily observable dilatation, frontal part bluntly truncated. 

 Tail about equalling half the length of the exposed part of the trunk; genital 

 segment comparatively large, being fully as long as the remaining part of the 

 tail, and oblong quadrangular in shape, with a well marked transverse suture 

 in the middle of the dorsal face; ovigerous spines about twice the length of 

 the tail. Caudal rami about equalling in length the last 2 segments combined, 

 and only slightly divergent, each provided with 5 strong plumose setae of 

 nearly equal size, the outermost one attached to a well-marked ledge of the 

 outer edge, the others to the somewhat obliquelly rounded apex. Eye imper- 

 fectly developed, without any trace of refracting elements, and only replaced 

 by a diffuse yellowish pigment. Antennae rather slender and elongated, though 

 scarcely exceeding in length the cephalic segment, and each apparently com- 

 posed of 5 joints, of which, however, only the 1st is distinctly defined, the 

 others being confluent and only indicated by slight constrictions of the antenna; 

 most of the setae attached around the middle of the fusiform terminal joint 

 reachly ramified. Oral tubule well marked and occurring somewhat behind the 

 middle of the cephalic segment. Natatory legs all of the very same structure and 

 also of about equal size; 2nd basal segment not very sharply defined from the 

 1st, and armed inside with 2 small juxtaposed denticles; terminal joint of outer 



