BULLAA. 289 
must not be supposed that this appendage is an epididymis 
connected with the testis, or a vas deferens, as there is a 
distinct groove for the latter use; it is the organ of repro- 
duction. We have some doubts if the shell of B. aperta 
be without a muscular attachment, as in dissection we have 
always seen, near the apex of the shell close to one side of 
the short columella, what appeared to be a delicate flat 
muscle springing from a subrotund scar; this is contrary 
to M. Cuvier’s dictum. The pedal locomotion is almost im- 
perceptible, and can only be appreciated by the fact that a 
space has been passed over. The natatory progress is more 
rapid. 
A review of these comparative observations appears fully to 
support the position, that m all essentials, and in many spe- 
cialties, this genus scarcely varies fron Bulla, and that Bullea 
is a happy appellation, differing so slightly from Bulla, as 
truly to represent the equally slight variations between the 
animals of the two genera. We may say that the differences 
are more apparent than real ; the mantellar membrane, passing 
over the shell instead of under it, beg of little importance ; 
in fact, it may be considered a tough epidermis, as under the 
shell there is a thin membrane of the nature of a pericardium, 
which may be substituted, without violence, for the visceral 
enveloping mantle of the typical Gasteropoda. Finally, we 
would ask, if it would not be conducive to the interests of 
science, and operate as a practical check to the enormous 
and useless multiplication of genera and species, to consider 
Bullea as superfluous, and its species a section of the genus 
Bulla? A re-examination and comparison of all the minute 
species of both tribes of this family with each other, and 
with those that have not as yet been seen, may require new 
genera; but as the case now stands, I think that Bulla and 
Bullea are sufficient. We all must object to the splitting 
and torturing mere specific differences to fabricate useless 
genera. 
