,284 Annals Entomological Society of America [Vol. XV^, 



Further backwards, behind the mound, a plate of very 

 variable size and form may be observed, which is known as 

 the "shield." It is not unusually found amongst Polydesmids, 

 Chordeumoids or Spirostreptoids, but has only been met with 

 in a single luloid Diplopod, Mesoblaniulus serrida, and its 

 existence in Paeromopus is highly interesting, {s, Figs. 4, 8, 9). 



Cephalad the mound is fenced in by the posterior wall of the 

 oviductal funnel; its anterior end is therefore flattened and 

 may be spoken of as the "anterior truncation." 



In front of the oviductal aperture is a more or less thickly 

 chitinised, erected plate (o, Fig. 5, 26, etc.), the posterior 

 surface of which is lined by the anterior wall of the funnel. 

 Its outline is variable and made to fit the anterior truncation 

 of the mound, whence the name "operculum" used for it. 



As a matter of fact, the vulvae are by no means as simple as 

 could be inferred from the above rough sketch; but the latter 

 will, perhaps, be sufficient from a morphological point of view, 

 and readers interested in further details will kindly refer to 

 Brolemann & Lichtenstein's paper of 1919. Yet a few more 

 words have to be devoted to a structure exceptionally met with 

 in some American species. 



When the vestibulum is deep enough to conceal the vulvae 

 and to allow the third segment to meet the second above 

 them, the operculum has very little importance as a protective 

 plate (see P. tiganiis). But when the summit of the vulva is 

 on a level with the ventral surface, the operculum is made to 

 shelter the mound from external contacts. For instance, in 

 contradiction with what has been so far observed in other 

 groups, the operculum of some of the species hereafter recorded 

 is by far the largest plate of the vulva, the most interesting 

 cases being those of the Paraiuli of the impressus group. In 

 these species the vulv^ are coupled, the opercula of both vulvas 

 having become coalesced into an uncommonly large, tectiform 

 plate, erected perpendicularly to the main axis of the body 

 {y, Figs. 39, 46, etc.), the only trace of fusion left being a 

 notch in the apical ridge ; consequently this plate will be spoken 

 of as a " synoperculum. " The mounds are located laterally 

 in distinct, symmetrical dimples bounded distally and inwardly 

 by diagonal edges of the operculum, delineating between them 

 and the apical ridge a raised, triangular or heart-shaped space, 



