PYBAMIDELLID^E. 403 



cleansed them from every particle of dried animal matter, a 

 difficult task from their minuteness ; I have them on tablets, 

 and shall be glad to show them to competent observers. 

 They are interesting from the fact, that Chemnitzia and 

 Jeffrey sia are the only marine Gasteropodan genera that have 

 these singular processes, except the Barleeia rubra, late the 

 Rissoa rubra, which, from its apophysis and testaceous lid, 

 has been shown above to be alien to Rissoa. The apophysis 

 is nothing more than an extension, sometimes from the 

 margin, but more usually, in Chemnitzia, springing from the 

 under surface, and appears to act as a clamp to strengthen 

 the closure of the operculum. This process is strikingly 

 conspicuous in Ch. conoidea and Ch. plicata, much more so 

 than in Jeffrey sia diaphana ; in Ch. acuta it approaches nearly 

 to the two latter species, but is not quite so marginal ; in Ch. 

 spiralis, Ch. decussata, and Ch. interstincta, it scarcely varies 

 from Jeffrey sia. 



The above generic diagnoses and peculiarities are absolutely 

 alike in all the animals of our tribe of Chemnitziee, whatever 

 may be the form of the shell : how then can we, at this epoch 

 of natural history, fall back upon exclusive and false concho- 

 logical indices in the formation of our families and genera, 

 such as, for example, the presence or absence of a tooth, the 

 smooth or sculptured shell, and thus throw overboard the 

 consideration of the soft parts and functional organs ? Are 

 variations of sculpture and a denticular point of almost in- 

 organic matter to outvalue the peculiar external organs of 

 the animal, as well as those internal ones which are the seat 

 of the nerves and of vitality? If these positions are true, 

 how can identical creatures be consigned to separate genera ? 

 Who will venture to draw a valid animal distinction be- 

 tween a Chemnitzia and an Odostomia? If this is impos- 

 sible, this singular tribe, united by so many ties, ought not 

 to form two divisions or genera. This is not my fiat; but 

 nature, reason, and the fitness of things forbid so unnatural 

 a disseverance. 



We thus see that the Chemnitzian animal, by its head para- 

 phernalia and cesophagean structure, is a compound one, 



2 D 2 



