426 Mr. G. C. Robson on the 
the head is usually not very much protruded beyond the shell, 
though one can generally see the eyes. The buccal mass can 
be seen working backwards and forwards if the animal is 
browsing. ‘The colorationis variable. Specimens have been 
found almost colourless, with two narrow bands of black 
pigment running backwards from the base of the tentacles. 
More usually this pigment is very dense on the head, muzzle, 
and upper and anterior parts of the foot, while on the sides 
and back of the foot it is less well developed. The foot-sole 
is invariably colourless except for the stripes referred to by 
Smith, 
Contrary to Smith’s statement, the animal is frequently 
seen floating on the surface-film (v. anon under “ Pedal 
Glands’’), and on one occasion it was observed to make use 
of this faculty in a peculiar fashion. If it is turned over on 
to the back of its shell it usually rights itself by rolling the 
front of its foot backwards over its head, getting a foothold, 
and pulling itself over by a leverage of the foot on the right- 
hand side of the shell-aperture. One was being prevented 
from doing this * when it suddenly stretched its foot upwards 
to the surface of the water and drew itself away from the 
detaining needle by this method. 
INTERNAL ANATOMY. 
The only substantial account of the anatomy of this genus 
of which the author is aware is by Henking (5) upon Hydrobia 
[=Paludestrina] ulve, Pennant. Henking’s paper and the 
present account do not cover the same ground, but, where 
possible, full comparison is made between the two forms, 
The Alimentary Canal. 
The mouth, when viewed transversely, presents the same 
general featuresas H. ulve. ‘The oral cuticle is not developed 
to the same thickness, however, while the vertical depth is 
greater in P. jenkinsi. The oral musculature does not corre- 
spond with that figured by Henking, the small dilators (ms) 
shown by him being absent in P. jenkinst. Separate elements 
corresponding with Henking’s lip-protractors are found. 
‘The jaws are situated much as in P. ulve. Henking does 
not describe them in detail. In P. jenkinsi they consist 
of about ten to twelve rather irregular columnar pieces of 
specialized cuticle, of which the median are the largest 
(Pl. AVe fied); 
Behind these the mouth expands laterally and is flattened 
dorso-ventrally over the lingual cartilages. Owing to the 
thick investment of muscle and the consequent difficulty in 
* In a watch-glass full of water. 
