136 



but the corresponding measurements of the other, that has a much smaller size, are placed 

 in parenthesis. 



Rostrum triangular, acute, twice as long as wide in the middle, reaching a little beyond 

 the extra-orbital angles, its lateral margins diverging backward and beset with short setae; 

 the upper side which is slightly curved downward, bears three longer setae near the tip. In a 

 lateral view the straight, lower margin of the rostrum appears to run horizontally forward. The 

 rostrum is continued backward as a low, rounded crest or carina that extends to the middle ot 

 the carapace, gradually disappearing; the crest bears four spiniform teeth, the first or hindmost 

 is the -smallest, the second and the fourth are of equal length, one and a half as long as the 

 first, while the third is slighdy longer than the second or the fourth. E.xternal angles of the 

 orbits rounded; at a short distance beneath them, the antero-lateral margin which is also 

 fringed with short setae, bears a small, subacute prominence that probably represents the 

 antennal tooth. Pterygostomian angle obtuse. The carapace is distinctly pubescent anteriorly, 

 perhaps also posteriorly. 



Abdominal pleura rounded posteriorly, except those of the 6'^ segment that are acute, 

 though not articulate or movable ; this 6'^ segment appears elongate with a rounded upper 

 border and just twice as long as thick, when looked at from above. 



Telson as in O. occidentalism but the lateral margins bear, just before the middle, an 

 obtuse prominence or tooth, which in the species from the river Tocantins is apparently wanting 

 (A. Ortmann, I.e. Fig. 42). The length of the telson equals 3,4-times the width of the posterior 

 margin, i. e. the distance between the postero-lateral angles, and the proportion between this 

 distance and the width at the base is 1,7^. Posterior margin as in O. occidentalism very prominent 

 and rounded, its length being three-fifths the distance between the postero-lateral angles ; the 

 longer, internal spinules reach as far as the extremity of the telson, but the outer are very 

 short. The spinules of the upper surface are small, measuring one-sixth the width of the posterior 

 margin and are rather far remote from the lateral margins; those of the anterior pair are 

 implanted in the middle, those of the posterior just twice as far from the end of the telson as 

 from the anterior pair. The outer uropods of the caudal fan are much longer than the telson, 

 narrow, curved outward and their extremity is acute ; the inner are still narrower, obtuse at the 

 tip and reach to midway between the end of the telson and that of the outer uropods. 



Unfortunately in this mutilated specimen the third antennular article with the flagella, as 

 well as the antennal flagella arc missing. The very slender eye-peduncles, that are thickened at 

 both extremities, reach with half the length of their black, facetted eyes beyond the extremity 

 of the second antennular article, but they are almost as much shorter as the carpocerite as the 

 eyes are long; the eye-peduncles are a little less than halt as long as the carapace, the length 

 of the latter being in proportion to that of the peduncles as i : 0,43. The first or basal anten- 

 nular article reaches to the middle of the eye-peduncles and, measured from the base of the 

 rostrum to the end of the article, appears just twice as long as the second or median article, 

 which is nearly 3-times as long as thick and rather .slender. Like in O. occidentalis Ortm. the 

 stylocerite terminates in two .strong, acuminate spines; the outer spine reaches to the distal fifth 

 part of the basal antennular article, the inner is a little shorter and slightly directed upward. 



4 



