514 Mr. R. I. Pocock on the Morphology 



pairs of appendages and abutting against the inner angles of 

 those of the sixth in front of the generative orifice, wliere it is 

 slightly [Gonyleptes) or considerably [Adceum) expanded*. 

 Tliis expaniled portion is overlapped by the genital plate, and 

 frequently the maxillary processes of the fourth pair overlie 

 its anterior portion in the middle line (OncopodidEe, Triaeno- 

 nychidffi, Biantida3, &c.), although it is uncovered iu the 

 Gonyleptidee and Cosmetidje. 



Borner has also, I think, misinterpreted the sterna of the 

 opisthosoma in Trogidus. The large plate following the 

 genital operculum is numbered 4 and the following plate 5 

 (fig. 11, p. 443), and it is to be inferred that these plates 

 correspond to those numbered 4 and 5 in the figures of Lepto- 

 psalis and Packyhis, the fourth being that which bears the 

 stigmata and the fiftii the next following. But in PachyJus 

 and, I believe, all Laniatores and most Palpatores, except 

 some Phalangiidffl (e. g., Sclerosoma), the sterna Borner 

 has designated 4 and 5 in the case of Pachylus are united to 

 form a single plate, the line of demarcation being represented 

 by a shallower or deeper groove or scared}' at all traceable. 

 In Trogulus the divisional line is, I think, quite obliterated. 

 If so, the sternal plate marked 4 by Borner for this genus 

 should have been marked 4 + 5 to bring it into harmony with 

 those of Pachylus, and the sternum marked 5 should be 6. 

 This method of enumeration arrives at numerical similarity 

 in the sternal plates in the two genera, instead of leaving 

 Trogulus with one plate short. Trogulus is an exceedingly 

 specialized genus, and the key to its morphology is to be 

 found in its less specialized allies Dicranolasma and Nema- 

 stoma. Both these genera have the same number of sternal 

 plates as Pachylus, namely, seven, including the genital and 

 the anal, and the second is marked by a transverse impression, 

 as in Pachylus and many other genera of Laniatores, indi- 

 cating its primitive double origin. I think there can be no 

 reason to doubt that this transversely impressed second plate 

 in Dicranolasma is the homologue of the unimpressed second 

 plate in Trogulus. 



In the Laniatores and Palpatores eiglit sternal plates are 

 to be traced with certainty. The first is the genital, the 

 second the tracheal, and the eighth the anal. In all Lania- 



* In the article " Arachiiida " in the supplementary issue of tJie 

 EncYcl. Britannica, p. .544 (190:2), under the heading Laniatores the 

 insei'tion of the words " of the fifth pair " was an error which was 

 overlooked in the correction of the proof. Also under the family Cryptu- 

 stemroidse (p. 543;, for Anthracomartvs read Poliocliera. 



