DECAPOD CRUSTACEANS OF THE WEST INDIES 61 



Remarks. — Large males oiA. innocous have the lateral lobes of the 

 rostrum subrectangular, approaching the subacute form in A. scahra, 

 but males of the two species can be distinguished easily by numerous 

 other characters. In living specimens, the two can be separated by 

 the color pattern, especially the transverse bands near either end of 

 the abdomen in A. scahra, and by the different texture of the integu- 

 ment. Atya innocous is much more slippery and more difficult to hold 

 in the hand than is the rougher A. scahra, even though the latter is a 

 more slender shrimp, the carapace especially being proportionately 

 less high than it is ui the former. The antennular peduncle, on the 

 other hand, is usually somewhat longer proportionately m A. innocous 

 than it is in A. scahra, and it lacks the one to three dorsal spines that 

 are usually present on the basal segment proximal to the distal 

 circlet in A. scahra (figs. 10a, d). The third pereiopod of A. innocous, 

 although much more robust than in A. lanipes, is normally more 

 slender than in A. scahra, especially in males of the two species, and 

 it is studded with appressed corneous scales, rather than with the 

 much more erect, though flat-topped, ciu-ved spines characteristic of 

 A. scahra. The appendix masculina on the second pleopod of the male 

 is provided with longer but fewer spines, particularly on the central 

 portion of the mesiodistal surface, in A. innocous than in A. scahra. 

 Probably the most rehable characters for separating males of the two 

 species are the form of the pre-anal carina (figs. 106, e) and the arma- 

 ture of the ventral margins of the abdominal pleura (figs. 10c, f). In 

 A. innocous, the latter consists, at most, of a short row of small, 

 acute denticles on the third, fourth, and fifth somites, but the pleura 

 of any or all of the somites may be unarmed, or the spinules may be 

 almost mdistinguishable from some of the stout hairs arising from 

 the pleural margins. In A. scahra the pleura of the second, third, 

 fourth, and fifth somites are armed with more extensive and more 

 prominent series of close-set, blunt, stout spines. Female and juvenile 

 specimens are more difficult to identify by any of these characters; 

 it is quite possible that some of the juveniles assigned to A. innocous 

 from the Dominica collections may be A. scahra. Females of A. scahra 

 can be identified by the form of the rostrum in the series examined; 

 the pleural armature is much as in males of A. innocous, but the 

 forms of the third pereiopod and of the pre-anal carina are reliable, 



Atya innocous was generally known as A. occidentalis until the 

 identity of Herbst's species was demonstrated by Holthuis (1966). 

 The western American material of Atya available to us is not sufficient 

 to determine the status of ^. tenella Smith, 1871, and we are therefore 

 foUo^sdng the suggestion of Holthuis in considermg it distinct from 

 A. innocous for the time being. 



