88 



Arc-torn* given by Latreille to another genus which has generally been regarded 

 as the type of the family. The name of the family should therefore perhaps 

 more properly be changed to Astaclllidce. The present genus is chiefly distin- 







guished from Arcturus by the greath. length of the middle segment of the meso- 

 some, which gives the body an extremely slender, nearly cylindrical form, whereas 

 in Arctnrus it is more fusiform in shape. Moreover the structure of the 1st 

 pair of legs is slightly different, and the incubatory pouch, which in Ardunts 

 is formed by 3 pairs of distinct lamella? issuing from the 2nd, 3rd and 4th 

 segments, is here only confined to the middle segment of the mesosome. The 

 genus comprises several species, amounting to about 10 in all. To the fauna of 

 Norway belong 4 species, to be described below. 



1. Astacilla longicornis (Sowb.) 



(PI. XXXVI.) 

 Omscus lonijiciHiils, SdAverliy, Brit. Miscell. T. 19. 



Syn : Lcacia lacertnsa. Jolmst. 

 ,. Arcturus longicorms, Westw. 

 ., gracilis, G<><><lsu- (male). 



tfjtt'cific (harnrtcrz. Body of female very slender, subcylindric in form, 

 and sculptured with obtuse tubercles. Oephalon produced on each side to a lingui- 

 form lobe extending forwards, and covering the bases of the' inferior antenna 1 , frontal 

 margin deeply emarginatcd, dorsal face with 2 juxtaposed obtuse prominences. 

 The first 3 segments of mesosome short and. when combined, scarcely exceeding the 

 cephalon in length, each with a rather slight dorsal tubercle, lateral parts of 1st 

 segment rather large and deep, triangularly produced in front, so as partly to 

 cover the oral area, those of the 2 succeeding segments rounded and extended 

 laterally. Middle segment of mesosome about twice the length of the preceding 

 part of the body, and covered with small obtuse tubercles, 2 of which placed side 

 by side in its most anterior part dorsally, are more conspicuous, lateral parts 

 confined to a small rounded lamella issuing from the segment on each side quite 

 in front. The 3 posterior segments of mesosome irregularly angular, and deeply 

 emarginated dorsally. Coxal plates of 1st segment obsolete, those of the 3 suc- 

 ceeding segments very small, and concealed beneath the lateral parts, those of the 

 3 posterior segments well developed, triangular, extending laterally. Metasome 

 about half the length of the mesosome, its 1st segment evenly vaulted above, last 

 segment conically tapering, and terminating in a long acuminate point. Eyes large 

 and convex, triangular in outline. Superior antenna 1 with the tlagellum about the 

 length of the 2 preceding joints combined, and carrying 9 olfactory filaments. 



