no. 1831. NEW TROPICAL MILLIPEDS—COOK. 471 



In other words, the true Oryptodesmidee of South America have 

 no close relationship with the African families Pterodesmidse and 

 Stylodesmidse. 1 



THE SYSTEMATIC POSITION OF CHATELAINEA. 



Though the structure of the gonopods shows that the affinities of 

 Chatelainea undoubtedly lie with Stylodesmidas and Hercodesmidse, 

 rather than with the Pterodesmidse, the radical difference in the 

 form of the body forbids the reference of the genus to either of the 

 related African families, both of which are characterized by strongly 

 convex segments, strongly depressed carinas, and longitudinal ridges 

 of large dorsal tubercles or processes. 



Chatelainea was compared also with the West Indian genera 

 referred to the family Chytodesmidas, for in some of these the form 

 of the body approaches that of Chatelainea, at least to the extent 

 that the segments are nearly flat, the carinas nearly horizontal, and 

 the dorsum without any specially developed tubercles or ridges. Two 

 such genera have been known for some years from the West Indies, 

 Docodesmus from St. Vincent and Tridesmus from Porto Rico. 

 Another genus from Porto Rico, hitherto undescribed, offers a 

 still closer approximation to Chatelainea, in that the carinse are 

 deeply incised instead of having the margins entire or slightly scal- 

 loped, a feature that distinguishes it at once from the other West 

 Indian genera of the group. 



The carinas of Iomus, as the new Porto Rican genus is now called, 

 are fully as wide or wider than those of Chatelainea, and more deeply 

 lobed. The lateral edge, in particular, is cut near the middle by a 

 very deep notch, often completely closed at the margin by the pro- 

 jecting connivent corners of the lobes. The other notches are also 

 partly closed along the edge, somewhat as in Chatelainea, but more so. 

 The anterior margin, entire in Chatelainea, is notched in Iomus like 

 the posterior margin, though not quite so deeply. 



The carinas of Iomus are strongly depressed, leaving the middle of 

 the body very convex instead of nearly flat as in Chatelainea. Four 

 longitudinal rows of distinctly enlarged tubercles ornament the 

 segments of Iomus, but are not developed in Chatelainea. Each 

 row is represented by three tubercles on each segment, the two 

 inner rows having somewhat larger tubercles than the outer, and 

 arranged with more regularity. The posterior tubercles of the 

 middle row, on segments 17, 18, and 19 are distinctly enlarged into 



i The family name Pyrgodesmidae Silvestri (1896) is used by Pocock in the Biologia instead of Btylo- 

 desmidse Cook (1895), on the ground of a conjecture by Attems that the generic name Stylodttmus if • 

 synonym of Urodesmus Porath, and therefore not available as the basis of a family designation. In reality, 

 Urodesmus is quite distinct from Stytodcsmus and more likely to belong to the Hercodesmidse than to th« 

 Stylodesmidae. At most it may serve to connect the two groups. This would not interfere with th« 

 utility of Stylodesmidse as a family name, but would only extend its application. 



