30 Rathbun — -Three New Species of Fresh-water Crabs. 



boundaries is drawn in fine wrinkles. The cervical suture if continued 

 would cross the orbital margin at its middle. The protogastric lobes are 

 small but prominent. The front is about one-fourth the width of the 

 carapace, deflexed, deepest in the middle, margin sinuous. The orbits 

 are inclined obliquely downward and outward (fig. 2); superior margin 

 sinuous and directed forward and outward, terminating at the outer angle 

 in a prominent acute tooth. Margin of front and superior margin of 

 orbit strongly rimmed. Inferior margin of orbit crenulate. Epibranchial 

 tooth small, tuberculate, situated as far from the tip of the orbital tooth 

 as half the width of the orbit; and succeeded on the lateral margin by 

 small irregular tubercles for about half the length of the branchial region. 

 Siibbranchial region visible laterally outside the branchial margin and cov- 

 ered with short oblique granulated ridges. Suborbital area comparatively 

 smooth, but with fine scattered granules ; jugal area coarsely tuberculate. 



The ischium of the outer maxillipeds (fig. 3) has a deep median furrow 

 and large punctse ; merus rougher, slightly longer than wide, and its an- 

 tero-lateral margin is obtusely rounded. The sixth abdominal segment 

 of the male (Jig. 4) is longer than the seventh and its proximal margin is 

 convex, so that the fifth segment is longer laterally than in the middle. 



Chelipeds very unequal. Men elongate; margins armed with strong 

 teetli ; lower surface near antero-distal angle furnished with a stout down- 

 ward projecting tooth. The carpi are covered with granulated rugae and 

 the inner margin is spinous, the distal spine much the larger; outer in- 

 ferior angle with a downward-pointing tooth. The propodi are coveted 

 with minute scabrous granules, among which are scattered larger gran- 

 ules set in punctse ; inner surface rougher than the outer. Pollex bent 

 down. Both fingers deeply grooved ; prehensile edges armed with very 

 irregular blunt teeth ; little gaping, the projections of the one finger in 

 general fitting into the cavities of the other. 



Ambulatory legs very long; meral joints compressed, upper margins 

 spinulous ; both margins of the propodal joints spinulous. 



Dimensions.— Length 23.5, width 32, exorbital width 20.2, posterior 

 width 23.2, width o'f front 8.8 mm. 



Type locality. — Mouth of Mesurado River, Monrovia ; 0. F. Cook ; one 

 male (U. S. Nat. Mus. No. 20(343). 



EXPLANATION OF PLATES. 

 Pl. I. Potamon abbotti. 



Fig. 1. Dorsal view, X f. 2. Front view, X i- 



3. Abdomen of male, X If. 4. Outer maxilliped, X If. 



Pi.. II. Potamon macropus and levicervix. 



Fig. 1 . P. macropus, dorsal view, X |. 2. Front view, X 



3. ( (titer maxilliped, X 1|. 4. Abdomen of male, X 1A. 



5. P. levicervix, dorsal view, X i- 6. Front view, X ]■ 



7. Abdomen of male, X |. S. Outer maxilliped, X f. 



