APLYSIA. BULLA. 



251 



closely resembles the last in its mantle, but is remark- 

 able for the body being beset with large, flat, irregular- 

 shaped and palmated membranes, as if it was overgrown 

 by sea weeds ; the tentacula are only two, and these 

 also are covered with similar processes as long as them- 

 selves ; there is no shell ; and the mouth, resembling a 

 small longitudinal slit, is placed beneath.* We have 

 no doubt that all these, hereafter, will be found to con- 

 tain sub-genera, some of which we may subsequently 

 characterise. 



(235.) In regard to the Bulling, we have already 

 stated our difficulties, as they 

 now stand in Lamarck's and 

 Cuvier's arrangements. Some 

 have external, some internal, 

 shells, thin or strong, horny or 

 calcareous, coloured or hyaline ; 

 in all these, however, the ovi- 

 form orbulla-shapeis uniformly 

 preserved. The annexed cut 

 from Guilding's drawings of a 

 species allied to B. aperta, will 

 show how nearly the animal is 

 related to the Aplysiance, while 

 it gives a correct idea of the 

 general character of such types 

 as have their shell concealed. 

 In the genus Doridium-f of Mecken, the shell almost 

 disappears ; according to M. Rang;]:, the two lateral lobes 

 of the animal are so much developed that they can be 

 used as fins. Many of the Bullinw have the gizzard 

 composed of bony pieces ; the tentacula assume the ap- 

 pearance of large, fleshy, angulated processes, under 

 which are very minute sessile eyes. 



* See Riippell's admirable figure of AWarcAMs/arinm^MS, Atlas, i. pi. 7. 

 fig. 2. 



f Akcra Cuv. 



t Manuel de U Hist. Nat. des Mollusques, p. 146. The reader will find 

 a great deal of original and valuable information in this unpretending but 

 excellent little volume. 



