438 F. A. I'OTTS. 



Tlie soil-iieuiatodes belonging to tliis genus differ widely 

 among themselves, particularly in respect of:' such definite 

 characters as the niiiiil)er and arrangement of the papillae on 

 the tail of the male. 'J'he typical nundjer is nine or ten pairs, 

 but D. gracilis Bi'itschii and othei-s have eight, and D. 

 robustus jNlaupas, eleven. 'JMie arrangement of the })apillae 

 is more variable than their numbiM', but in a snjall group of 

 species, with which 1 am more specially concerned here, the 

 relative positions are fairly constant and characteristic. 



The arrangement of the ])a})illa3 follows the scheme given 

 below. The numbers correspond to those given in the various 

 diagrams (see Text-fig. 4). 



(1) A pair of papilhe opposite the antei-ior end of the 

 copulatory spicules. D. robustus Maupas possesses an 

 extra pair, situated far in front of the spicules. In D. mau- 

 pasi sp. n., as a frequent variation one of this pair may have 

 been shifted forward to a markedly pre-spicular ])osition. 



(2, 3) Two pairs of papilhe opposite the posterior end of 

 the copuhitory spicules. 



In U. robustus Maupas shows th ree pairs in this position. 



(4) One pair slightly post-spicular. 



(5, 6) Two pairs, the anterior situated about half-way 

 between the root of the tail and the anus, and the posterior at 

 the root of the tail. 



(7-9) I'hree small pairs at the root of the tail, more ventral 

 than the last-named. 



Since, then, there is so mnch similaritv between the members 

 of the group, the species are best distinguished by differences 

 in size, proportions and biology, to which they are remark- 

 ably constant. 



Common Characters of the Gi-oup. — Buccal cavity 

 surrounded by lips with short seta3. Within two^ chitinous 

 teeth. Vulva situated in middle of bodv.~ 



' Some species of Diplogaster. for instance D.fictor Bastiau, 

 possess only one bnccal tooth. 



^ D. gracilis Biitsclili has a " monoliysteroiis " ? orgr.n ^vith the 

 vulva a slioi't distance antei'ior to the anus. 



