SOME LITTORAL OLIGOCHATA OF THE CLYDE. AZ 
with the camera lucida, shows that the setee have in this particular instance blunt, in some 
cases almost square, ends, and are without trace of a distal curvature; their proximal 
ends, however (with the exception of the innermost seta but one), show a gentle and 
gradual curvature, not the somewhat sharp curve seen in the genus Enchytreus. The 
figure was drawn from a specimen in glycerin, and since the setal bundles are not per- 
fectly flattened, their two ends are at different levels and there is, perhaps, some optical 
distortion. This, however, will not apply to the single seta drawn in fig. 6, b: this was 
found in a section mounted in the usual way in balsam; it belongs to segment iv., and 
was drawn with the camera under an oil immersion lens. It will be seen that its distal 
portion is perfectly straight, and that it has a hooked inner end, the shape being that 
Fic. 6.—a, group of sete from an anterior segment of Lwmbricillus viridis. 
b, straight seta from segment iv. of a specimen of Luwmbricillus viridis. 
characteristic of the genus Hnchytreus. Such “straight” setee therefore do occur in 
the anterior part of the body, in the present form. 
Fig. 7, a, shows two setze of a posterior bundle, drawn with a camera under an oil- 
immersion lens; the ends of the setee are obliquely pointed as in Lwmbricillus, not 
with the straight points seen in the genus Hnchytreus. 
I tried the effect of potash on the worms; but they are so stout and firm that a 
strong solution of KOH has to act on them for hours before they collapse and flatten so 
as to present the setal bundles in one plane; the setee then appear swollen and have 
evidently lost their true shape. Nevertheless, a double curvature of the Lumbricillus 
type, though not to be recognised in most of the anterior sete, is then. often fairly 
obvious in the setee of the posterior bundles. Thus fig. 7, b, shows two setze of a posterior 
bundle in which this curvature is quite obvious; and fig. 7, c, shows a fairly distinct 
double curve in a seta as far forward as segment viil. 
As supporting the view of the affinity of the sete with the Lumbricillus rather 
than with the Hnchytrzus type, the fact of the difference in length of the setze of a 
TRANS, ROY, SOC. EDIN., VOL. XLVIII. PART I. (NO. 2). 8 
