276 Mr. R. I. Pocock on the Pedipalpi of the Family 



upon the second abdominal sternite of most of the Old-World 

 species of the group. 



The sexes may be always recognized without difficulty. 

 Beneath the genital operculum in the male there is a pair of 

 soft, muscular, weakly chitinized, indistinctly bisegmented, 

 apically bifid organs, w r hich probably function as penes, and 

 may be homologous to appendages *. When the operculum 

 is raised these organs protrude from the aperture. In the 

 female, on the contrary, there are no protrusible organs like 

 the penes beneath the operculum, but there is a pair of rounded 

 membranous eminences affixed to the lower surface of the 

 operculum, each one bearing a pointed, inwardly directed, 

 chitinous claw-like rod. That specimens possessing this 

 structure are females is shown by the fact that they carry egg- 

 sacs and that no specimens of those with the penes have been 

 found with young. Moreover, the latter possess as a rule 

 longer palpi and limbs, characters which by analogy appertain 

 to the male {vide PI. VII. figs. 8, 8 a). 



In some of the Old- World genera of this group these sub- 

 opercular structures are not so easy to determine. 



Genus Tarantula, Fabr. 



Synopsis of the Species contained in the Collection of the 

 British Museum. 



a. Tibia of the chela armed above with 9 spines, 



of which the third from the proximal end and 



the fourth from the distal end are the longest 



there being two spines between those just 



mentioned. 

 a 1 . The spines on the chelae longer, the longest 

 on the tibia longer than the width of this 

 segment ; the fourth and fifth spines from 

 the proximal end of the upper edge of the 

 tibia very unequal in size, owing to the 

 smallness of the fifth ; median ocular tu- 

 bercle larger, higher than the lateral eye- 

 clusters ; frontal process less covered. 



* The possibility of there being a direct homology between these 

 organs and the missing pectines of the scorpions should be borne in mind. 

 I have already suggested (Ann. & Mag. Nat. Hist., Jan. 1893) that the 

 fact of there being an abdominal sternite missing in the Pedipalpi, the 

 tergites being numerically one in excess of the sternites, might perhaps 

 be explained by the enlargement and backward growth of the genital 

 operculum over the second sternite, which in scorpions bears the pectines. 

 If this has taken place, remnants of the pectines might be retained 

 beneath the genital operculum, where, in fact, these penps of Phrynvs are 

 situated. 



