87 



peculiar structure of the 4 anterior pairs of legs. The family comprises as yet 

 3 genera, viz., Arcturus, Astacilla and Arctnrclla, the last 2 of which are repre- 

 sented in the fauna of Norway, and will he treated of helow. 



Gen. 1. AStacilla, Cordiner, 1795. 



Syn : Lcacid, Johnston. 



Generic Characters. Body extremely slender, suhcyliudric in form, with 

 the middle segment of mesosome very much elongated, heing in male narrow cy- 

 lindric, in female somewhat thicker, and carrying heneath it the incubatory pouch. 

 The 3 posterior segments of mesosome short and very movably articulated, so as 

 to allow the anterior part of the body to be bent dorsally at right angles to the 

 posterior. Metasome with only a single segment distinctly separated in front of 

 the terminal one, which is conically produced behind, and exhibits at the base 

 on each side a small projecting lappet, really indicating the presence of an- 

 other imperfectly defined segment. Eyes large and prominent, lateral. Superior 

 antenna; with the tlagellum more fully developed in male than in female, and in 

 both sexes carrying a number of delicate olfactory filaments arranged along the 

 outer edge. Inferior antenme very much elongated, though having the flagellum 

 extremely short, and only composed of 3 articulations finely denticulated inside, 

 the last terminating in a small spine. Maxillipeds with the palp well developed. 

 5-articulate, epignath comparatively small, basal part in female produced in a thin 

 ciliated plate extending posteriorly. 1st pair of legs densely setous, proximal 

 part of dactylar joint lamellarly expanded; the 3 succeeding pairs very slender, 

 and fringed with a double row of long seta?, dactylus obsolete. The 3 posterior 

 pairs of legs smooth, dactylus strong, bidentate at the tip. Uropnda with the ter- 

 minal piece triangularly pointed, secondary lamella very small, setous at the tip. 

 Incubatory pouch only formed by a single pair af elliptical valvular lamella- 

 issuing from the middle segment of mesosome. 



Remarks. As stated by the Rev. Mr. Stebbing, the generic name Asta- 

 cilla, which has generally been attributed to Fleming, was in fact proposed at a 

 much earlier date (1795) by the Rev. Charles Cordiner to designate a species of 

 the present genus. The name Leacla proposed by Johnston in 1825, and used 

 by some subsequent authors, was merely abandoned, because a very similar name, 

 that of. Leachia, had been previously applied to a genus of Cephalopods. In any case, 

 the name Astacilla should be given the precedence, as it is still older than the name 



