624 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvm. 



Grooves separating the carapace areas considerably different from 

 those in other species. The two longitudinal grooves forming the 

 sides of the "H" are strongly inclined toward each other anteriorly, 

 and there are two crossbars instead of one, dividing the length of the 

 carapace into quite even thirds. Eyes very small and situated just in 

 front of the anterior crossbar. Free thorax segment subtriangular in 

 shape and a little more than half the width of the genital segment. 



Genital segment obovate, not quite half as wide as the carapace, 

 with broad and well-rounded posterior lobes. Abdomen spindle 

 shaped, half the length of the genital segment, with a strongly 

 emarginate posterior margin. Anal lamina? large and curved in well 

 toward each other. 



The characteristic of the appendages is great length, combined with 

 a reduction in width, making them appear very slender. The first 

 antennas are somewhat of an exception to this rule; they are slender, 

 but are also very short and hardly show at all on the anterior margin. 

 But in the second pair the terminal hook is nearly twice the length of 

 the basal joint and is bent into an almost perfect sickle shape. 



Both pairs of maxilke are much elongated and narrowed, the 

 branches of the second pair diverging considerably. The terminal 

 claw of the second maxillipeds is longer than the basal joint and 

 strongly curved, but its accessory spine is small and weak. 



The furca is much elongated^, with widely divergent and slender 

 branches, which are somewhat enlarged at the very tips, but these 

 tips are not acuminate in American specimens, as was noted by Baird 

 in European specimens; they are rather blunt. 



The first three pairs of thoracic legs are normal; the fourth pair 

 have a spine at the outer distal angle of every joint and three terminal 

 ones. The two largest of these latter are very distinctly toothed. 

 The fifth pair of legs, which are ordinarily rudimentary papilla?, are 

 in this species quite broadly foliaceous, but they do not protrude far 

 from the ventral surface. 



Total length, 10 to 12 mm. Length of carapace, 5.5 mm.; width of 

 the same, 5.1 mm.; length of genital segment, 2.85 mm.; length of 

 abdomen, 1.5 mm.; length of egg strings, 7 mm. 



Color a dark yellow-white, without pigment spots of any kind. 



Male. — Carapace a little longer than the rest of the animal and itself 

 longer than wide, narrowed anteriorly and quite strongly convex. 

 Frontal plates rather more distinct than in the female; frontal margin 

 slightly rounded with a broad notch at the center. Free segment much 

 longer and narrower than in the female, about one-fourth the length 

 and one-fourth the width of the carapace; considerably widened at the 

 center through the bases of the fourth legs. Genital segment acorn- 

 shaped, longer than wide, much narrowed anteriorly and deeply emar- 

 ginate posteriorly; furnished with two acute lobes on either side at the 



