201 



126. Attheyella gracilis, G. 0. Sars. 



(PI. CXXX). 

 Cantliocamptm gracilis, G. O. Sars, 1. c. p. 22. 



Syn: Canthocamptus inornatus, Scott. 



Specific Characters. Female. Body exceedingly slender and elongated, 

 linear in form, with the two chief divisions of almost equal length. Cephalic seg- 

 ment narrowly rounded in front, rostral projection very small. Caudal segments 

 without distinct whorls of spinules at the hind edge; last segment of about same 

 length as the penultimate one, and having the anal opercle finely ciliated at the 

 edge. Caudal rami slender and narrow, being more than twice as long as they 

 are broad, and slightly tapered distally, tip narrowly truncated, apical setae of 

 moderate length and only slightly divergent, setse of outer edge remote from the 

 apex. Anterior antennae rather slender, being only very slightly dilated at the base, 

 terminal part almost as long as the proximal one. Posterior antennae with the 

 outer ramus small, not attaining half the length of the terminal joint. 1st pair 

 of legs with both rami narrow, the inner one the longer and 3-articulate, with 

 the 1st joint a little shorter than the other 2 combined. Natatory legs with the 

 outer ramus much narrower than in the preceding species, that of 4th pair very 

 slender and elongated. Last pair of legs with the distal joint rather small, oblong 

 in form, inner expansion of proximal joint very slight and provided with 4 slender 

 setee. Ovisac oblong in form, with a very limited number of ova arranged in a 

 single layer. Spermatophore, attached to the genital segment, narrow lageniform. 



Male much smaller than female and exhibiting the usual sexual differ- 

 ences. 3rd pair of legs of much the same structure as in the male of A. crassa, 

 but less strongly built. Inner ramus of 4th pair with the number of setse much 

 reduced. Last pair of legs exceedingly small, proximal joint without any setifer- 

 ous expansion inside. 



Body semipellucid, of a light yellowish red colour. 



Length of adult female 0.70 mm. 



Remarks. This form is at once distinguished from any of the other 

 species of the present genus by its very slender and narrow body. The structure 

 of the last pair of legs is also rather characteristic. 



Occurrence. I have met with this form occasionally in the neighbourhood 

 of Christiania, as also in some other places of the southern part of the country. 

 It is generally found near the edges of small lakes with rich vegetation. 



Distribution. Sweden (Lilljeborg), British Isles (Scott), Germay (Schmeil), 

 Holland (v. Breemen), North America (Herrick). 



