Hirudinea. 165 
Three specimens. "Body exceptionally soft. Enormous quantities of mucus pro- 
duced. Adhering to lower surface of stones." 
Systematic Position. In spite of the peculiar external appearance this leech be- 
longs undoubtedly to the distichodont division of the family Hirudinidae, as shown 
by the presence of two rows of teeth on each jaw. It is closely allied to the genera 
Haemopis and Semiscolex, and forms together with these a well-defined group. The 
three genera may be distinguished as follows: — 
Furrows all alike, jaws with about 30 teeth . . Haemopis. 
no jaws .. .. ., Semiscolex. 
Furrows unlike, jaws rudimentary . . . . Myxohdella. 
It is noteworthy that in specimens of Semiscolex variabilis from Southern Patagonia 
studied by Percy Moore (1913) the furrows separating the annuH in a somite are of 
different depths so long as the animal is young, but the inequality disappears when 
it is full grown. Here too, as in Myxohdella , the deepest furrow is that between the 
third and fourth annuli, so that there are formed two natural groups of annuli, con- 
sisting of I, 2 and 3, and 4 and 5 respectively. If carefully examined when young, 
a similar condition might also be found in some other genera. 
In the rudimentary condition of the jaws our leech exhibits certain affinity with 
the African genus Trematobdella , which, according to the investigations of Johansson 
(1909, 1914) carries rudimentary teeth in a position corresponding to the jaws of the 
Hirudinids. In other respects, however, this genus shows all the essential characters 
of Herpodellidae, including the so-called pseudognaths, not found in other families. 
Fam. HERPOBDELIvIDAE. 
4. Herpobdella testacea (Savigny). 
Syn. Nephelis testacea, Savigny, 1820. 
Nephelis vulgaris y Moquin-Tandon , 1826, partim. 
Herpobdella octoculata, Blanchard, 1894. 
Locality. Komatsu, Lake Biwa, ca. 30 ft. Oct. 27, 1915. One specimen. On 
external surface of living Corhcula shell. Colour. Dark, dull purplish grey, paler 
towards extremities." 
This is a very small immature specimen, measuring only 13 mm. in length and 
1-5 mm. in width. It has only six eyes instead of eight, the middle ones of the 
second row being absent. 
In the identification of this species I have followed Johansson (1910) who states 
that the form commonly known under the name of H. octoculata is in reality H. tes- 
tacea of Savigny. 
It may be noticed here that this is the less abundant of the two species of Her- 
pobdella found in Japan, the other one, H. octoctUata, Linne {H. atomaria, Blanchard, 
1894) being by far the commonest of all the freshwater leeches of this country. 
