Paludestrina Jenkinsi, Smith, and P. ventrosa, Mont, 377 
evident. The transverse rows of teeth are slightly more 
arched in P. ventrosa than they are in P. Jenkins’; in the 
former, moreover, the admedian teeth alternate with and 
project slightly between the central ones, whereas in the latter 
they are nearly in a line with, and stand clear of, the median 
teeth, so that the whole radula has the appearance of being 
more sharply divided into longitudinal areas. The contrast 
between the respective median teeth is yet greater. In P. 
ventrosa the central cusp of the rachidian is as long as_ half 
the width of the tooth, and is flanked on either side by three 
others, whilst the single basal denticle on each side is barely 
visible ; in P. Jenkins?, on the other hand, the length of the 
central cusp is not more than one third the width of the whole 
tooth ; four or even five minor cusps flank this central one to 
right and left of it, and four basal denticles stand out conspi- 
cuously on either hand below the crest of the tooth. 
Portion of Radula of :—A. Paludestrina Jenkinsi, Smith 
B. Paludestrina ventrosa, Mont. 
Two rows of teeth are in each case shown on the left of the median 
tooth in their undisturbed position, On the right the teeth of a single 
row are drawn apart. 
The remaining differences are best seen from the figures. 
The following brief descriptions, with approximate micro- 
measurements, of the radulee of these two species are founded 
on several specimens of each. 
