402 PYRAMIDELLID#. 
loped at the anterior and upper part of the foot in most of the | 
Chemnitzie ; 1t is a plain bilobed flap of the skin, separating 
the sole of the foot from the upper area, and has no connection 
with the so-called mentum. The rostrum, as I term it, is 
longer than the foot; but if it were an offspring thereof, one 
would suppose that such a condition could not exist; it, and 
its circular, bilobed, or spatulate disk, lie on the foot of the 
animal in full march, and, in every species I have examined, 
invariably precede it considerably. This is also the case with 
the muzzle of the Rissoe. I speak confidently of the pre- 
cession of the rostrum in Chemnitzia. This fact is very 1m- 
portant, as it shows that this organ in that genus, and the 
muzzle of the Littorinide, are always carried on the march in 
a similar position, whereas in the Muricide the very short 
head, or anterior portion of the neck, is always borne poste- 
riorly to the foot. For the reasons stated, I must consider the 
organ called the mentum as essentially distinct from the foot 
as the rostrum of the Rissoe, fully justifying M. Philippi, M. 
D’Orbigny, and Mr. Lowe in stating, and, as I think, rightly 
describing it as “ proboscis abbreviata, depressa, infra tenta- 
cula exserta.”” The rostrum, though mute anteally as an organ 
of deglutition, is nevertheless the remaming vestige of the 
Littorinidan lineage of this transition Muricidal animal. All 
the Chemnitzie have the rostrum varying in shape in the 
different species. 
The opercula of the Chemnitzie are generally suboval or 
pyriform, and a compound of corneous and testaceous matter. 
They are all characterized by an apophysis, at about the centre 
of the inferior surface, nearest to the marginal notch for the 
tooth when there is one, and the nucleus shows its upper 
position. This process is usually more testaceous than the 
other portions of the operculum. The arrangement of the striz 
shows some variations, but this is not uncommon in the same 
genus in other families, and may be seen even in the same 
species ; for instance, in Trochus lineatus some have fine spiral 
strize, so close-set as to appear concentric ; some have radiating 
lines, and others are as grossly spiral as in the Littorina littorea. 
T have examined fourteen species, having, with great trouble, 
