Earthworms of the Vienna Museum. 127 
not lettered as clitellum; but no other structure is shown in 
the drawing which could be supposed to be the clitellum. 
And Schmarda states in the text that the clitellum is usually 
situated behind. The structure which Schmarda has mistaken 
for a clitellum is really nothing of the kind; it is formed 
(fig. 8a) by a group of segments of a somewhat tumid appear- 
ance which project beyond the general surface of the body, 
such as Fritz Miller first described * in Urocheta corethrura. 
This remarkable point of similarity first directed my attention 
to the probable identity of Pontoscolex and Urocheta. 
‘The clitellum, as a matter of fact, is anterior in position. 
Schmarda noticed that this was the case with some specimens. 
The error into which he fell is to be accounted for by the fact 
that in the specimen figured, as in many of those collected by 
him, the clitellum was not developed. In those individuals 
in which it is developed it occupies eight segments com- 
mencing with xv. Its extent therefore is precisely that of 
Urocheta, or, as it must now undoubtedly be called, Ponto- 
scolex corethrurus. Schmarda counts seven sete only in each 
segment, which alternate in position in successive segments 
from the very first. ‘This enumeration is inaccurate ; there 
are undoubtedly eight sete per segment on most of the seg- 
ments; occasionally on some of the posterior segments of the 
body Iecould only find seven, but this is most probably merely 
due to the loss of one seta. As to the alternation, this only 
occurs in some of the specimens; perhaps as this fact is the first 
distinctive point mentioned in the description of the genus I 
should refer to that genus the individuals which I describe 
later as Diacheta littoralis. As, however, that fact is not 
referred to in the description of the specdes, and as the figure 
seems to me to bea little more like the individuals possessing 
a clitellum of eight segments, I think that the name “ areni- 
cola”’ should be applied to them. 
In this species, then, the setee do not alternate from the very 
beginning; upon the first few segments (I am not certain 
how many) they are strictly paired; the two sete of each 
pair are quite close to each other. In this the species 
resembles Pontoscolex corethrurus. But, unlike what is found 
in that species, the setee are ornamented, as in Lhinodrilus, 
with a series of curved ridges. In Pontoscolex corethrurus 
some of the sete are ornamented, viz. those upon the clitel- 
lum; in Pontoscolex arenicola the clitellar are also orna- 
mented, but they only differ from the sete of the preclitellar 
* “ Description of a new Species of Earthworm,” Ann. & Mag. Nat. 
Hist. vol. xx. 1857, p. 15. See also my own observations upon the same 
structure in the same journal for January 1891, p. 95, 
