28 PROCEEDINGS OF THE NATIONAL MUSEUM vol. hi 



until the entire dorsum is merely coriaceous to smooth. Peritremata 

 moderate in size, set near the center of the paranota, about five 

 times the diameter from the lateral margin and four times the diameter 

 from the caudal margin. Paranota of segment 19 large, oblong 

 lobes, slightly divergent, extending back to middle of epiproct. 

 Latter large and robust, nearly parallel sided, with the caudal margin 

 slightly convex, the dorsal tubercules pronounced. 



Anal valves nearly flat and granular, with two setiferous tubercules 

 on each, the uppermost of which is in contact with the mesial marginal 

 ridge of the valve. Preanal scale (hypoproct) large and inflated, 

 strongl}^ overhanging ventral margin of anal segment, distally pro- 

 duced into two high, conical paramedian tubercules. 



Ventral sides of paranota and pleural areas finely granulate, 

 smooth. Podosternites strongly elevated and produced conically 

 near the base of each leg. Basal leg joints nearly glabrous, the 

 distal-most rather densely setose; the joints in decreasing order of 

 length 3-6-2-5-4-1; tarsal claw rather small, straight, polished. 

 Legs 4-7 with a rather high and acute conical sternal process at the 

 base of each; the coxae with a small field of large bristles adjacent 

 to each of these knobs. 



Coxae of gonopods rather large, the surface smooth but for three 

 short macrosetae on the dorsal side and a smaU field of a dozen or so 

 short bristles on the mesial face. Teiepodite basally short and 

 straight, slightly constricted just proximad of the midlength, there- 

 after broadening again; the distal third bent over the coxite forming 

 a right angle with the rest of the telopodite; solenomerite moderately 

 long and sinuate; apex of tibio tarsus drawn out somewhat but dis- 

 tinctly truncate and itself bent at nearly a right angle. 



Remarks: On the basis of gonopod structure, Nyssodesmus attemsi 

 seems most closely related to A^. tristani and A^^. antius, and in fact 

 the three forms may eventually prove to be only geographic races 

 of a single species. It differs from these two congeners, as well as 

 from the others, in having the dorsal tuberculation best developed 

 anteriorly, the caudalmost segments becoming virtually smooth. 

 The type specimen, unfortunately, is completely discolored from the 

 preservative, so that we have no idea what the color pattern in life 

 might be. 



This is the first species of Nyssodesmus to be recorded from Panama, 

 most of the other species occurring in Costa Rica. Presumably the 

 genus is a fairly recent segregate from the original Platyrhacus stock 

 that crossed the Panamanian Isthmus and that is still represented in 

 Costa Rica and Panama by several species. 



