ON THE PAIRED NEPHRIDIA OF PROSOBRANCHS. 593 
2. Trochus turbinatus, Born. 
The topography of the pericardium and kidneys is practically 
the same in Trochus as in Haliotis; Turbo is so nearly 
allied to Trochide that I think it unnecessary to give a full 
description of this form. My friend Mr. Macbride and myself 
have dissected two large specimens of Turbo, and have found 
that it differs but very slightly from Trochus, and these 
differences are so small that they may be neglected entirely 
with regard to the points which form the subject of this 
memoir. 
Haller has made the same erroneous statements about 
Turbo as about Haliotis, which have already been corrected 
by Perrier, with whose observations my own agree perfectly. 
When the mantle cavity has been opened by a longitudinal 
section parallel to the attached side of the only remaining left 
ctenidium (Bl., fig. 4), and viewed from the ventral surface, 
the rectum (R.) is seen in the shape of a long tube opening 
into the mantle cavity (JZ) by the anus (A.), which is situated 
at about the fifth of the total length of the gill from its 
proximal end. To the left (in reality the right) of the rectum 
the duct of the right kidney is seen as a long tube opening into 
the mantle cavity by an orifice (Xr.). To the right (in reality 
the left) another wider tube is to be seen, which does not 
run parallel] to the rectum as the duct of the leftkidney. This 
tube or sac is the left kidney, which also opens into the mantle 
cavity by a button-hole-like orifice (X/.). The left kidney or 
papillary sac extends back to the pericardium (Pc.), which has 
been opened in order to show the two auricles of the heart. 
The axis of this organ is oblique to the longitudinal main axis 
of the body—a fact which is already apparent in Haliotis, but 
to a lesser degree. 
In a series of transverse sections beginning at the anus, or, 
better, at the point at which the rectum issues from the peri- 
cardium anteriorly, and extending back to the point at which 
the rectum issues from the pericardium posteriorly, a large 
sinus (das., fig. 13) can be discerned lying ventrally to the 
