The true first abdominal Sternite 19 



line pi'ojects to the transverse strip and a shorter line to the lateral free part of the arculi), 

 but in Gagrelld and Sclerosonia is separated from them by a narrow groove with soft skin, 

 into which the lateral margin of the apex of opercnlum genitale fits when the opening is 

 closed. From this strip the other portion {n) of the transverse piece extends forwards and 

 downwards as a perfectly free projecting lamina which entirely hides that part of sternum 

 which cannot be reckoned as forming the labium'. Hidden by this free portion of the 

 transverse piece a narrow strip of soft skin is found between its front basal margin and 

 sternum. The anterior border of the piece is sometimes rather convex {Gagrella minax Thor.), 

 in other cases rather emarginate in the middle, as in Phalangium. To us it is beyond doubt 

 that this hard transverse strip with its appended free lamina is not at all, as Simon thinks 

 (b, PI. XXL, fig. 4), the sternum-, but that it corresponds to the inward bent ends of arculi 

 genitales in Cyphophthalmi. The correctness of this view is confirmed by the structure in 

 Ischyropsalis. It is true that in this genus arculi genitales do not appear as a separate 

 portion of the fourth coxa ; but under and partly in front of the anterior extremity of 

 operculum genitale there is a rather short hard transverse piece, of which the anterior margin 

 is thicker than the rest; it is not expanded into a freely projecting lamina as it is in Phalan- 

 gioidte, but, like the corresponding piece in that family, it is separated from sternum by a 

 groove with soft skin ; at the lateral corner the transverse piece is bent backwards, and 

 continued on either side as a rather narrow strip under the lateral margin of operculum 

 genitale, along the fourth coxa with which it is fused. In Nemastoma and Trogxdus arculi 

 genitales are likewise invisible outside operculum genitale. In Neiuastuina a nearly square 

 piece is found between the first pair of coxae from the posterior margin of which a pair of 

 strips extend backwards along the proximal ends of the three posterior pairs of coxge, with 

 which it is connected by thinner though well chitinized skin. We look upon this square 

 piece with its two continuations as representing sternum and arculi genitales together; labium 

 being, as before mentioned, separated from sternum by quite soft skin. In Trogulus (woodcut 

 fig. T) the structure is the same as in Nemastoma in all respects except that the plate 

 formed by the coalescence of sternum and arculi is triangular and proportionally larger, so 

 that its posterior margin is situated a little behind the proximal extremity of the third coxa. 

 In Trogulus the lower interior margin of the fourth coxa terminates in a small lobe, which 

 in part projects independently and is situated inside and in front of the proximal end of 

 the third coxa; this lobe recalls the lobe-like anterior corner of that part of arculi genitales 

 which in Phalangioidae is visible out.side operculum genitale, and the fact points to the 

 conclusion that the interior margin of the fourth coxae also in Trogulus morphologically 

 belongs to arculi genitales^. 



In Laniatores arculi genitales are very inconspicuous ; all that as a rule can be seen of 

 them is a slightly curved low chitinous ridge to which operculum genitale fits, when the 

 latter is closed, as a lid to a box, whereby the ridge is quite hidden from sight. Like arculi 



' See our statements on this subject above (p. 8) in sternal plate" is the front part, as belonging to the abdomen, 



treating of sternum. because their real nature cannot be seen without a close 



- We can only suppose that Simon did not perceive the comparative study of the whole sub-order Palpatores together 



true sternum itself. with Cyphophthalmi. But in consequence he, for instance, 



" Pocock, in his recently published paper on the Moi-phology did not see the real sternum in PhalangioidiE, which is con- 



and Classification of the Opiliones (<(), attributes great weight cealed by his "second sternal plate" (PI. IX., lig. l.-l " .<( 2"). 



to the structure of sternum in Palpatores. It cannot be A further consequence of the last-named fact is that he did 



chargeable against him that he did not arrive at the right not apprehend the real differences in this region between the 



conception of our " arcuh genitales," of which liis " second different groups of Palpatores. 



3—2 



