Anatomy of Paludestrina jenkinsi. 429 
aré thinner than those of the ventricle, and there is a capacious 
efferent branchial vessel. No very satisfactory sections of 
the auriculo-ventricular orifice were obtained. In the best, 
however, distinct traces of modifications of a valvular nature 
were found (Pl. XV. fig. 6), comparable in general to tie 
condition figured by Moore (8) for Zyphobia. At the posterior 
apex of the ventricle the anterior and posterior aorte are given 
off quite close together. The first runs forward across the roof 
of the pericardium for a good distance, and then, following 
the cesophagus, passes into a large lacuna. The posterior 
aorta passes backwards into a similar lacuna situated between 
the stomach and intestine. Branches of an artery were found 
ramifying in the ovary and uniting to form a single trunk at 
about’ the same level as the commencement of the oviduct. 
The two run parallel for a long distance down the columellar 
region. ‘This genital artery appears to run into the abdo- 
minal lacuna referred to above [¢f. distribution of the poste- 
rior aorta in Cyclostoma elegans (Garnault, l. ¢.)]. 
The Excretory System. 
A single kidney is found bounded by the posterior wall of 
the pallial cavity, the pericardium, and the body-wall; it 
opens into the first-named cavity by a short, narrow, ciliated 
canal. Making all due allowance for contraction, there is no 
trace of a ureter such as is found in Paludina and Valvata. 
The kidney is rather triangular in section over most of its 
area, and its walls are slightly folded. Its distribution and 
relationships are as yet uncertain, but it appears to give off 
a posterior thin-walled prolongation which ramifies among the 
other organs. 
The Reproductive System. 
The animal is apparently parthenogenetic (v. supra). 
The ovary is situated as usual in the apical whorls, though it 
does not appear to extend to the actual summit. It is closely 
applied to the liver, and can usually be seen contrasting in 
colour with the dark hue of the latter. It lies on the rigiit of 
the liver in each whorl, and extends downwards and inwards 
on the columellar (right-hand) side. It consists of a number 
of anastomosing tubules which finally unite in the oviduct. 
‘The contents of these tubules vary with age and condition, 
but, save in the very smallest specimens, one usually finds a 
certain number of developing odcytes of various sizes. A 
quantity of yolk-globules is almost always seen in one or two 
of the largest tubules. This yolk is sometimes the only 
contents of the latter. It would seem that there is a special 
localization and concentration of yolk, though it is also found 
