ON THE PAIRED NEPHRIDIA OF PROSOBRANCHS. 595 
dissections, it can be clearly seen that the portion of the peri- 
cardium leading into the reno-pericardiac duct is a longish 
prolongation extending ventrally and anteriorly to the heart. 
Its position corresponds to that of the reno-pericardiac duct 
already described in Haliotis. 
The right kidney, the properly secreting part of which is to 
be seen in fig. 12 (Vr.) below the urine chamber, does not com- 
municate either with the pericardium or with the left kidney 
or papillary sac. There is avery short true genital duct 
in Trochus and Turbo. The gonad which lies quite close 
to the right kidney discharges its products into the mantle 
cavity, as v. Jhering has already stated. 
3. Fissurella, Emarginula, Puncturella.! 
These species, differing exceedingly slightly in the general 
appearance, position, and histological texture of both kidneys, 
can be all described at a time. 
I examined five different species of Fissurella, viz. the four 
different species which are to be found in the Gulf of Naples, 
that is to say, Fissurella costaria, Bast. (=mediterranea 
=europea), Fiss. greca, Linné, Fiss. nubecula, L., and 
Fiss. gibberula, Lamarck. I also dissected a Chilian species, 
which I believe to be the Fiss. maxima. 
I think that a few hints concerning the determination of 
the four species found at Naples may prove useful, as I found 
considerable difficulty in determining them with the diagnoses 
given by conchologists. 
Fiss. costaria, also called reticulata, is the largest 
species, and can attain a length of 4 to 5cm.; the shell, which 
anteriorly is narrower than posteriorly, is provided with about 
twenty well-marked ribs diverging from the fissure; between 
these ribs there are several others less well defined. Fiss. 
greca is generally about half the size of the species which I 
have just described, the shell is just as broad in front as 
behind, the ribs are all about the same size, and formed by a 
succession of scale-like processes of the shell, which make it 
1 Pelsener (22) has found the left kidney in Scutum (Parmophorus). 
