NEOTROPICAL PLATYRHACID MILLIPEDS — HOFFMAN 29 



Psammodesmini, new tribe 



The genus upon which this group is founded differs from other 

 Neotropical platyrhacids in the relationship of the terminal gonopod 

 elements. The tibiotarsal blade is thin and laminate, but is directed 

 either continuously distad in line with the femur or is bent in the 

 direction away from the coxa. The solenomerite is derived from the 

 coxal side of the telopodite and in direct line with the course of the 

 seminal groove, but is bent adcoxally parallel to the direction taken 

 by the tibiotarsus. 



The tribe includes only the single genus Psammodesmus Cook. 



Genus Psammodesmus Cook 



Psammodesmus Cook, 1896b, p. 53. — Hoffman, 1953a, p. 301. 



Type: Psammodesmus cos Cook, by original designation. 



Range: Cordilleran Region of northwestern South America, from 

 northeastern Peru to the Isthmus of Panama. 



This generic name was revived in one of my recent papers (1953a), 

 which endeavored to account for all of the known species apparently 

 referable to it. However, the valid claims were overlooked of 

 Platyrrhacus atratus Chamberlin, which was described in 1947 from 

 specimens taken in southwestern Colombia. The locality alone 

 should have drawn attention to the form as a possible representative 

 of Psammodesmus. Although the formation of the gonopod telopodite 

 reflects differences of at least tribal value between the genera Platyr- 

 hacus and Psammodesmus, the structure cannot be clearly observed 

 unless the gonopod is examined from the mesial aspect. Psam- 

 modesmus atratus, as illustrated in the original description, could not 

 therefore be referred to either of these genera. To correct this short- 

 coming, a drawing (fig. le) made from the holotype is provided 

 herewith for comparison with those given in one of my earlier papers 

 (1953a). 



Psainmodestnus atratus (Chamberlin), new combination 



Figure le 



Platyrrhacus atratus Chamberlin, 1947, p. 34, fig. 12 (type data given as holotype, 

 male, ANSP 9958, 300 miles up the Atrato River, Colombia). 



This species is the largest now known in Psammodesmus; it has a 

 maximum width of about 13 mm., whereas the other forms range 

 from 7 to 11 mm. wide. In most other characters, however, it agrees 

 well with them. The ozopores are removed from the lateral margin 

 by a distance of about four times the diameter of a peritreme; none 

 of the paranota are indented or incised adjacent to the pore as in 



