W. A. Harding 
141 
posterior sucker, the dark pigment upon its upper surface disposed in a 
more or less distinct cruciform pattern, in the central portion of which 
are situated the two pairs of eyes. Posterior sucker ovoid, about twice 
the width of the extended body, with fourteen dark rays and a para- 
marginal series of fourteen black oculiform spots. Colour greenish, 
yellowish or brownish, usually finely sprinkled above and below with 
minute black or brown stellate pigment cells, which are disposed more 
or less regularly in longitudinal and transverse rows. The body is 
marked with eight rows of generally elliptical white spots, viz. a pair 
of marginal rows and, dorsally and ventrally, a single median row 
situated between a pair of intermediate rows. The spots composing 
the dorsal median and the two marginal series are the largest and 
distinguish the first rings (in the middle portion of the body, usually 
the first four rings) of each somite. 
All these spots are subject to considerable variation in form and in 
the extent to which they are developed. Frequently they tend to fuse 
into transverse bands in the anterior part of each somite ; the three 
ventral series are the least conspicuous and may be more or less 
obliterated. 
The first eleven somites of the posterior region of the body (XIII— 
XXIII) are complete with fourteen rings and each of them is provided 
with a pair of pulsating vesicles which, in diastole, arch up the skin of 
the first four rings. The male genital orifice lies in somite XI, usually 
distinguished above by an irregular white blotch, often extending over 
the whole of its dorsal surface ; the female opening lies in somite XII, 
which under certain conditions may become constricted. Somites 
I—IV and the anterior portion of V, which is distinguished by a 
white transverse band, are included in the anterior sucker. Somites 
VII, VIII and IX are complete. The anus opens in the posterior part of 
somite XXVI. The seven pairs of rays and oculiform spots seen on the 
posterior sucker correspond to the seven somites XXVIII—XXXIV of 
which it is composed. These observations however require revision. 
Dimensions. The English living examples which I have examined 
measured as follows: 
Length 20—30 mm.; width 1'5—2 mm. 
Larger dimensions appear to be attained. Brightwell’s specimens 
(1842) were “from one to two inches long”; the measurements given 
by Johansson (1909) are, 20—50 mm. long and 12—5 mm. wide. 
