208 
W. A. HASWELL. 
beset on the inner aspect with a row of sharp denticles, four 
in number on the outer tooth, ei«-ht on the inner. All four 
ramules of each ramus are connected together by articula- 
tions, so that they act together in the movements ot: protru- 
sion and biting. 
The jaws of S. novae- hollandiae differ from those of 
S. tas manic us in certain respects. In most cases, as 
already mentioned, the entire apparatus is considerably 
longer in the former than in the latter. The individual 
chitinous parts also present definite and constant differences. 
The most marked of these concerns the broad plate which 
terminates each o£ the lower jaws in front. The anterior 
margin of this plate, provided with about six irregular 
denticulations in S. tasmanicus (fig. 16), is in S. novee- 
hollandiee (fig. 17) marked with a deep, rounded incision 
near its inner margin, followed by a comparatively large 
tooth, which is separated by a shallow notch from a second, 
much smaller tooth. 
The muscles of the jaws have been described in Histrio- 
b dell a by Shearer and in Stratiodrilus by myself, and the 
agreement between the two genera is fairly close. The chief 
muscles in Stratiodrilus are in three sets. One of these 
represents what Shearer calls in Histriobdella the bulb- 
like muscular organ of the jaws.^’ In Stratiodrilus I des- 
cribed it as a pair of large bundles of non-striated fibres, 
each of which is wrapped round the ventral side of the corre- 
sponding lower jaw, the fibres running forwards parallel with 
the latter throughout their (its) length. These two muscles 
are in close apposition with one another along the mid- ventral 
line, separated, however, by a thin septum of nucleated 
material continuous with the lining of the head coelom, of 
which it appears to be a thickening. They are continuous 
with the retractor fibres behind. The ventral edge of each 
is unfolded, and becomes continuous with the ventral edge of 
the corresponding muscle of the second pair — to which 
account has to be added the statement that these muscles are 
continued from the lower jaws almost vertically upwards to 
