BULL^EA. 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 in all essentials, and in many spe- 

 cialties, this genus scarcely varies fron Bulla, and that Bullaa 

 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, being 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 

 Bullcea 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 

 Bull&a are sufficient. We all must object to the splitting 

 and torturing mere specific differences to fabricate useless 

 genera. 



