NOTES ON THE IIISTRIOBDELLID.E. 
199 
propose for the former the name Stratiodrilus novas- 
hollandias. The chief diiferences are in the jaws and, 
perhaps, the excretory system. The jaws are usually con- 
siderably longer in proportion to the size of the head, so that 
when retracted they project backwards some distance into 
the following or neck ^^-segment. In the minute structure 
of the jaws with their teeth there are also some constant 
points of difference, which will be referred to later. There 
is also a difference in the form of the chitiuous penis as shown 
in figs. 20-25. In S.tasmanicus it has its three basal 
processes more widely spread and is thinner at the base than 
in S. nov^e-hollandise. 
I prefer to postpone any further attempt to determine the 
relationships of the Histriobdelli dee with other groups of 
animals until I am in a position to give an adequate account 
of the development of Stratiodrilus, for which I have 
now obtained a good deal of material. 
External Features of Stratiodrilus; Movements. 
Stratiodrilus nov^-hollandiie is of similar size to S. 
tas manic us (about 1 to 1*5 mm. when full grown), and 
resembles it closely in both external features and internal 
structure. It consists of a head, which is a little less than a 
sixth. of the total length, five body-segments, and an imperfectly 
segmented tail region. The first of the body-segments, which 
is shorter than the others and bears no cirri, may be dis- 
tinguished as the neck-segment. As in S. tas manic us, the 
second, third and fifth segments bear each a pair of two- 
jointed cirri, both of which are provided with non-motile 
sensory cilia. The head bears the same appendages as in 
S. tasmanicus, viz. a median tentacle, two pairs of lateral 
tentacles and a pair of retractile anterior legs. The tentacles 
are all on the average relatively shorter than in the 
Tasmanian form, more especially those of the second lateral 
pair. The fourth segment in both species bears no append- 
ages in the female, while in the male it bears the retractile 
