BY VERA A. IRWIN-8MITH. 799 



winter of 1916, in material collected at Vaiicluse, on the rocks 

 between, and just below tide-marks. Since then, about thirty 

 worms of the same species have been obtained from the same place; 

 but extensive searches, in other localities, have proved fruitless. 



The ventral, adhesive setje are very powerful, and it is difficult 

 to dislodge the animal from its support, so that I have been al)le 

 to observe only five living individuals. These were taken fi-om 

 the concentrated washings of some thirty jars of fresh material. 

 Two of the worms were kept alive in a crystal-dish, with two 

 changes of sea-water, for a period of eight days, and a third for 

 nine days. They have the characteristic, creeping mode of 

 locomotion of the Cha'tosomatida?; and are more easily distin- 

 guishable from marine Nematodes when alive, than after death. 

 When fixed, the general appearance of the body so closely 

 resembles that of a small Nematode, that it is only possible to 

 detect them by means of the minute setic on the head and 

 ventral surface. 



The largest individuals attain a size of l"Omm., but the 

 average size is somewhat less than this, from 0'8 to 0*9 mm. 

 Male and female appear to be of the same length. The shape 

 assumed, when fixed, is not constant; but the posterior third of 

 the body is usually sti-aight, while the region in front is more or 

 less arched in a dorsal direction. The anterior end is only 

 slightly enlarged, and is distinguishable as a head-region by its 

 curvature, rather than by any definite neck-constriction. It is 

 usually more or less bent in a ventral direction, but the curva- 

 ture varies considerably in different specimens, as will be seen 

 in the Plates. The cuticle covering the body is very thick, and, 

 from the rostrum to the beginning of the tail, is transversely 

 striated. There is no special banded area behind tlie rostrum, 

 the strife being all broad and deep, of the same thickness all over 

 the body, though there is a difference in character between the 

 stride of the head-region and those behind, the former overlapping 

 one another, from behind forward, to a much greater extent 

 than the strife on the trunk (Fig. 53, cut.). The rostrum (Figs. 48, 

 53, n), is short, 0*014 to O'OlSnnn. long; and the smooth cuticle 



