238 



BULLETIN" 15 8, UNITED STATES NATIONAL MUSEUM 



KET TO THE SPETIBS (BOTH SEXES) 



1. First endopod 2-segmented ; basal expansion of fifth legs longer 



than distal segment, with 6 setae in female, 3 in male_ lilljeborg'i (p. 238) 

 First endoped 3-segmented ; basal expansion of fifth legs as long 



as distal segment, with 5 setae in female, 2 in male pygmaea (p. 239) 



MESOCHRA LILLJEBORGI Boeck 



Figure 158 



Mesochra liUjehorgi Boeck, Forh. Vid.-Selsk. Christiania, 1864, p. 275. — Sabs, 

 Crustacea of Norway, vol. 5, p. 208, pi. 135, 1906. 



Occurrence. — Both sexes found in moderate numbers in one of the 

 brackish ponds on Chappaquiddick Ishtnd, and in Quisset Pond, 

 Falmouth, July, 1926. 



Distribution. — Coast of Sweden (Lilljeborg) ; British Isles 

 (Brady) ; Kiel Bay (Giesbrecht) ; coast of France (Canu) ; Nova 



Zembla (T. Scott) ; coast of Nor- 

 way (Boeck, Sars) ; Adriatic (Car, 

 Pesta). 



Color. — Body transparent with 

 a whitish tinge; ovary and ovi- 

 ducts bluish green ; eye bright red. 

 Female. — Body about four times 

 as long as wide ; cephalic segment 

 as long as the three following seg- 

 ments combined; urosome three- 

 fifths as long as metasome, its seg- 

 ments fringed with spinules along 

 their posterior margins; caudal 

 rami nearly as wide as long. First antennae 7-segmented, shorter 

 than the cephalic segment ; exopod of second antennae linear ; exopod 

 of first legs shorter than basal endopod segment, the middle segment 

 with an inner seta; basal segment of first endopod sometimes with 

 two inner setae. Distal segment of fifth legs roundecl-oval, with 

 five setae, the middle terminal one filiform ; basal expansion tongue- 

 shaped, reaching far beyond the tip of the distal segment, with six 

 setae, the third outer one the longest. Total length, 0.6-0.7 mm. 



Male. — The four basal segments of the first antennae much en- 

 larged and densely setose, the three distal segments curved like a 

 claw ; distal segment of third endopod with two unequal apical setae 

 and a curved inner spine; fifth legs much smaller than those of the 

 female, the two segments often fused and about the same length, the 

 distal segment with fifth setae, the basal expansion with three setae. 

 Total length, 0.5-0.6 mm. 



Remarks. — Sars designated this as a littoral form, often left in 

 tide pools. It can be recognized by the 2-segmented endopod of the 



Figure 158. — Mesochra Ulljeiorgi: a. Fe- 

 male, fifth leg ; b, male, endopod of 

 third leg ; c, male, fifth leg 



