ATOPETHOLID MILLIPEDS — HOFFMAN AND ORCUTT 103 



tergite subdivided into 12 smaller sclerites in 3 transverse series of 

 4 each. 



Cook's observations were made upon specimens of Pachybolus, an 

 African genus belonging to the same suborder as the Atopetholidae, 

 and a newly moulted specimen of Narceus, a genus of the suborder 

 Spirobohdea. We can confirm his account with the notice of identical 

 segmentation in a newly moulted specimen of Eurhinocricus (Rhino- 

 cricidae) from Jamaica, and in several adult and hardened specimens 

 of Arinolus and Centrelus in the Atopetholidae. In brief, there is a 

 small elongate pleurite on each side, shghtly narrower than the 

 sternite, above which the tergite is divided into three transverse belts 

 by two sutures. There is furthermore a median dorsal suture across 

 all three transverse belts, and one such sutiu:e on each side at the level 

 of the pores. If the familiar usage of prozonite and metazonite is to 

 be preserved, it must be corrected and amended by the addition of 

 the intermediate belt, which can be designated as the mesozonite 

 (new term). It will now be into the mesozonite that the pore opens 

 when it is in front of the second suture, not into the prozonite. A 

 diagram (fig. l,c) is provided to indicate segmental composition, which 

 is shown as a flattened strip with the segment broken on one side at 

 the pleurosternal suture. 



In the Trigoniulidea, apparently the more primitive of the two 

 suborders on the basis of this segmental composition as well as 

 gonopod characters, much of the subsegmentation is visible in normal 

 adult specimens, particularly in Centrelus and in Arinolus. In the 

 more specialized Spirobolidae, the sutures are obliterated in adults, 

 and evident only in specimens not completely calcified. The presence 

 in spiroboloids of a distinct middorsal suture is a corroboration of the 

 primitive natm-e of the order as already indicated by the retention 

 of posterior gonopods and the presence of an eversible "penis" 

 terminating the vasa deferentia. 



Typically the surface of the pleurotergites is smooth and polished, 

 usually with a scattering of very fine punctations. In some forms, 

 such as the species of Onychelus and Arinolus, the surface of the 

 metazonites is somewhat inflated and raised above the preceding 

 subsegment, and may differ from it in microsculpture. In most 

 cases the prozonite is provided with a number of fine encircling 

 striae, as is normal for spiroboloids. The lower ends of both pro- 

 zonites and metazonites, and often also the pleurites, are ornamented 

 mth a very fine reticulum of beaded striae enclosing polygonal areas 

 that become elongated higher up on the sides and gradually merge 

 into the transverse striae. In nearly aU forms the lower sides of the 

 metazonites are provided with short longitudinal striae or the ventral 

 edges of impressed grooves; in several species these elevated areas 



