580 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



154. Rostrum triangular, as wide as long; body stout and pyriform; 



end segment of fifth leg reaching its entire length beyond 



basal expansion; muddy bottom, shallow. 



cf 9 Stenhelia Boeck, 1864 (p. 228) 

 Rostrum narrow, longer than wide; body slender, cylindrical; 



end segment of fifth leg reaching but little beyond its basal 



expansion; littoral, among algae cf ? Parathalestris Brady, 1873 



Rostrum obtuse, wider than long; body broad, depressed; 



end segment of fifth leg reaching two-thirds beyond 



basal expansion, with 4 setae; littoral, in sand. 



cf ? Machairopus Brady, 1883 



155. Fifth legs of female enormous, entirely covering ovisac, of 



male smaller, basal expansion slight, armed with 2 unequal 



setae; littoral, among algae cf ? Phyllothalestris G. O. Sars, 1905 



Fifth legs of female large, but covering only proximal end of 



ovisac, of male small, basal expansion armed with 3 setae 156 



156. Body strongly depressed, shield-shaped; no rostrum; end 



segment of fifth leg three times as long as wide; caudal rami 



wider than long; moderate depths cf 9 Amenophia Boeck, 1865 



Body not shield -shaped; rostrum present; end segment of 

 fifth legs fohaceous in female, twice as wide as long in male 157 



157. Caudal rami narrow, four times as long as wide, divergent, 



without lateral setae; body subcylindrical and large; 



pelagic, surface tow cf 9 Halithalestris G. O. Sars, 1905 (p. 202) 



Caudal rami not more than twice as long as wide, and parallel, 



with lateral spines or setae •_ 158 



158. Exopod of second antenna 3-segmented; rostrum prominent 



and mobile; caudal rami twice as wide as long; second endopod 

 modified in the male; moderate depths, among algae. 



cf 9 Rhynchothalestris G. O. Sars, 1905 

 Exopod of second antenna 2-segmented; rostrum smaller, but 



mobile; caudal rami as long as wide or longer 159 



Exopod of second antenna 1-segmented; rostrum very small, 

 immobile; caudal rami little wider than long; second endo- 

 pod not modified in male; littoral, among algae. 



d" 9 Nitocra Boeck, 1865 (p. 240) 



159. Body slender, compressed laterally, urosome nearly as wide as 



metasome; fifth legs of moderate size; rostrum large, mobile; 



littoral, tide pools cf 9 Parathalestris Brady, 1873 



Body stout, often depressed, metasome wider than urosome; 

 fifth legs large, sometimes covering half the ovisac; rostrum 

 immobile; littoral, among algae.- & 9 Thalestris Claus, 1863 (p. 201) 



160. Exopod of second antenna 1- or 2-segmented 161 



Exopod of second antenna 3- or 4-segmented 165 



161. Endopod of second antenna 2-segmented, exopod attached to 



side of basal endopod segment and itself 1- or 2-segmented 162 



Endopod of second antenna 3-segmented, exopod attached 

 to distal corner of basal endopod segment, and itself 



2-segmented 163 



Endopod of second antenna 3-segmented, exopod 1-segmented; 

 end segment of fifth legs three times as long as wide, both 

 margins fringed with hairs; muddy bottom, 60 fathoms. 



9 Argestes G. O. Sars, 1910 



