DESCRIPTIONS OF GENERA AND SPECIES 397 



in accordance with the number of spermathecae. The various groups defined with the 

 help of this character do not agree in other particulars. 



(9) The spermiducal glands vary greatly in size in the present genus ; they are 

 even, though very rarely, altogether absent ; in P. hilgendorfi there seems to be not 

 the least trace of them ; and in P. nipponica they are reduced to the muscular duct 

 into which opens, as usual, the sperm-duct. In other species they show a lesser or 

 greater degree of lobulation and extend through more or fewer segments ; in P. tapro- 

 banae the glands are so small that they are quite confined to one segment. The 

 muscular duct of the spermiducal gland sometimes opens directly on to the exterior 

 and sometimes indirectly thi-ough a dilated sac ; the latter condition is to be found 

 in P. indica and other species ; I refer to it in connection with the genital papillae. 



(10) The last character which is subject to variation in the genus is the number 

 and position of the specially-thickened septa. 



The following table gives the principal characters of the known species of 

 Perichaeta. I have not included P everetti and the few others which resemble it in 

 being so near to P. stelleri. 



In the following list and descriptions of the known species of Perichaeta (including 

 a few. described here for the first time) I have not followed any particular order or 

 grouping. Of so many species our knowledge of important characters is wanting ; 

 and it appeared to me that no good would be gained by a systematic arrangement 

 which could not be complete, and would probably be erroneous. On the other hand, 

 it would not be of much use to group the species which are fairly thoroughly known 

 as to all the characters made use of, since that would give the impression that the 

 remaining species were not identifiable ; and this impression would be quite wrong. 



The genus Perichaeta is pre-eminently a tropical genus, and is especially abundant 

 in the Old World, particularly in Asia and the East Indies. Of the seventy species 

 enumerated in the following pages only P. elongata, P. pallida, P. ringeana, P. ber- 

 mvdends, P. harhadensis, P- hesperidum, are exclusively New World ; a few species, 

 viz. P. indica, P. sumatrana, P. posthuma, P. houUeti, P. dyeri, have been received 

 from both quarters of the globe ; and there are, of course, a few doubtful American 

 forms enumerated in the list of unidentifiable species (on p. 397). Africa is so poorly 

 oflF in species that only two have been thence described, viz. P. capensis and P. dyeri ; 

 and both these species occur also elsewhere. 



Australia is as nearly barren of true Perichaeta; only three, P. queemlandica, 

 P. darTileiends, P. peregrina, have been described from that continent. P. vitierisis, 

 P. indica, P. upoluensis, P. grubei, P. novarae, P. hawayana are inhabitants of the 



