426 W. A. HASWELL. 
absence of a “ frontal organ,” as well as, probably, in other 
points, differs so widely from the other members of the group 
that it requires to be designated by a new generic name. I 
propose to call it Heterochzrus, and the species H. 
australis. 
It occurs in shallow rock-pools between tidal limits in Port 
Jackson towards high-water mark, and is most abundant in 
places in which it is exposed all day, without shelter of any 
kind, to the full glare of the sun. The breeding period 
extends throughout the summer and autumn months— 
November to May—specimens collected in October were 
sexually immature, while in June the sexual apparatus appar- 
ently undergoes degeneration, and soon practically disappears. 
The worms were best fixed by running the water off them, 
and subjecting them in an almost dry condition to the action 
of the vapour of osmic acid. This kills most of them very 
soon without producing much contraction. They may then 
be treated with Flemming’s strong chromosmic-acetic solution 
or with Hermann’s solution, or with a_picro-acetic-osmic 
solution. Hermann’s solution, followed by Merkel’s, gave 
some good results, but on the whole the picro-acetic-osmic 
combination was the most successful. Solutions containing 
sublimate (including Lang’s and Gibson’s formule) did not 
yield satisfactory results. Sabussow’s (24) modification of 
Kultschitzky’s photoxylin-paraffin method, with some altera- 
tions, proved entirely satisfactory for this brittle class of 
objects. 
The largest specimens are about 4 mm. in length, 1°5 mm. 
in greatest breadth. The body (fig. 1) is compressed dorso- 
ventrally, thickish towards the middle line, thin at the sides, 
tapering to a blunt point in front, deeply excavated behind, 
and frequently unsymmetrical. Only in one case, among the 
very numerous specimens examined, have I found the thin 
lateral margins folded back on the dorsal surface after the 
fashion which prevails in Convoluta. 
Locomotion may be effected by steady gliding through the 
water, usually in close contact with the solid substratum, 
