402 PYEAMIDELLID^:. 



loped at the anterior and upper part of the foot in most of the 

 Chemnitzite ; it 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 Rissoa. I speak confidently of the pre- 

 cession of the rostrum in Chemnitzia. This fact is very im- 

 portant, as it shows that this organ in that genus, and the 

 muzzle of the Littorinida, are always carried on the march in 

 a similar position, whereas in the Muricidce. 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 Rissoce, 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 remaining vestige of the 

 Littorinidan lineage of this transition Muricidal animal. All 

 the Chemnitzice have the rostrum varying in shape in the 

 different species. 



The opercula of the Chemnitzia 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 striae 

 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 

 striae, so close-set as to appear concentric ; some have radiating 

 lines, and others are as grossly spiral as in the Littorina littorea. 

 I have examined fourteen species, having, with great trouble, 



