372 PROCEEDINGS OF THE NATIONAL MUSEUM vol. us 



One of the structures that has been used in applying the name 

 appendage to the postantennal process is the nodule, arising from 

 the platelike area of sclerotization, which Heegaard (1947) calls 

 "the basal joint" of the first maxilla. In both the male and female 

 of D. litus there is a nodule bearing hairlike processes (as do all three of 

 the nodules of the postantennal process) on the dorsal anterior lateral 

 surface of the cephalo thorax, just posterior to the division between the 

 frontal region and the cephalothorax (fig. 10a) and well separated 

 from any appendage or process. Its presence in this position on 

 D. litus, however, implies only that a nodule of this type does not 

 necessarily have to be found in association with a process or an 

 appendage. 



The female postoral process of D. curtus is simple and not bifurcate 

 while that of D. ulua, D. hifurcatus, and D. litus is bifurcate. The 

 male postoral process of D curtus is not bifurcate while, as in the fe- 

 male, that of D. ulua, D. bifurcatus, and D. litus is bifurcate. In the 

 male of the last three species, however, a poorly sclerotized acuminate 

 or dactyliform process arises from the inner margin of the inner 

 tine at the level of the apex of the bifurcation. 



A pair of small but distinct adhesion pads on the ventral cephalo- 

 thoracic sm-face of the male of D. ulua extends posteriorly and medi- 

 ally from the region of the distal end of the postoral process to the 

 region just posterior to the mouth cone. Distinct indications of this 

 adhesion surface appear on the male of D. litus and indistinct indica- 

 tions of it on the male of D. bifurcatus. D. curtus is the only species 

 in which the male does not exhibit any indication of these adhesion 

 surfaces. 



The basic structures comprising the maxilla — the two segments, 

 two saber-shaped terminal processes, and the membrane on the second 

 segment — are similar in all four species. The interspecific differences 

 in this appendage are caused by the presence or absence of an acces- 

 sory structure — a spine or spine-shaped process found in the region 

 of the sharp indentation in the middle of the second segment, and by 

 the minor differences in segment shape. D. ulua and D. curtus pos- 

 sess the membrane common to all four species but do not possess the 

 spine, while D. bifurcatus and D. litus possess both the membrane and 

 the spine. 



The maxilliped, like the maxilla, is basically similar in all four 

 species, the only major difference being the presence or absence of a 

 distally indented swelling on the inner surface of the male appendage. 

 The male of D. ulua, D. bifurcatus, and D. litus all possess this swelling 

 while the male of D. curtus does not. 



The sternal furca of D. ulua has chisel-shaped tines while the sternal 

 furca of all of the other species has pointed or rounded tines. In ad- 



