764 ON THE CH^TOSOMATID^,, 



which it is beset; and the general shape which the worm tends 

 to assume, when fixed. 



In all species hitherto described, the head-area is clearly dis- 

 tinguishable into three regions. 



(1). The frontal part, known as the rostrum, on which the 

 cuticle is not striated. This, as a rule, bears the anterior "head- 

 hairs" or setae, and a pair of curious, laterally situated, spiral 

 grooves. 



(2). The middle part, always the narrowest of the three regions, 

 which is ringed by cuticular striations, much coarser and more 

 strongly marked than on any other part of the body. 



(3). The hinder part, only distinguishable from the trunk by 

 its greater thickness, and the "neck"-constriction which marks 

 it off from the latter. 



But in two of the New South Wales species now^ described, 

 there is little or no demarcation of a head-region. The pharynx 

 lacks the typical, swollen "bulbs," and, in consequence, the 

 anterior end of the body is very little, if at all, enlarged. The 

 worm can be distinguished from a Nematode only by the rows of 

 ventral setae, and its characteristic creeping mode of locomotion. 



The absence of a head-swelling would seem to suggest that 

 these worms are more nearly allied to lihahdogaster{2, 10) than 

 to Chcetosoma. But, in the general structure of the body, they 

 difi'er considerably from Bhabdoyaster, and are very similar to 

 other species af Chcetosoma. There is no median constriction of 

 the trunk; the ventral seta? are stout, hollow rods, with distal 

 segments, not delicate and crook-like, as in Rhabdoy aster; and 

 the female genital pore and genital organs are situated in the 

 anterior, not the posterior half of the body. 



I have, therefore^ placed these two worms as a new genus, 

 N otochcetosotna, in the family Chcetosomatidce. The typical 

 rostrum is present in both species of K otochcetosQtna^ but there is 

 no special "banded" area of coarsely striated cuticle behind it. 

 This banded area is also absent in one of the New South Whales 

 species of Chcetosoma, described as C. falcatum. 



The number of rows of ventral, locomotor setae is of consider- 

 tible systematic importance. All four New South Wales species 



1 



