two Genera of Molluscous Animals. 33 



which are picked up dead. The small species for safety should be glued on 

 blackened card. I do not observe that the fissure is always dorsal ; in my 

 specimens it is either lateral or ventral. 



Of the place of DentaUum in the natural system I will not venture to speak 

 at this moment, though perhaps we shall not do wrong, in the present state 

 of our knowledge of the Mollusca, in placing it near the great family, or, I 

 should rather say, great tribe of Linnaean Patelloe. In its anal opening it 

 resembles the genus Fissurella, while the apical fissure represents the poste- 

 rior marginal rima of Emarginula. 



Tlie substances figured by Mr. Sowerby in his accurate illustrations of the 

 Genera of Shells, fig. 9, are in no way connected with Dentalia, though I 

 do not pretend to determine their real nature. Their closed mouth and the 

 connecting corneous ligaments are very curious. I have lately dredged up, 

 among sea-weeds, numerous specimens of an animal {Oikodomicus, Guild.) 

 much more analogous in outward look to the true Dentalia. The habitacu- 

 lum is diaphanous, tubiform, vitreous, slightly bent, symmetrical, having the 

 termination softer but not attenuated. It does not possess the hard calca- 

 reous body of the shells before us ; but if Cuvier himself had received the 

 empty habitacula, he might have thought them good Dentalia. The animal, 

 however, is not affixed, but is closely related to Nereis. It is a most singular, 

 active and entertaining animal in its captivity, and shall be fully noticed here- 

 after. 



MOLLUSCA. 



Statio generis in systemate adhuc dubia sistit, at forsit^n prope Emarginulas. 



Genus. Dentalium. Auctorum. 

 Animal arenicolum, valdfe elongatum, testae figuram exhibens, dorso arcuato. 

 Corpus anticfe truncatum, postic^ mollius, subdiaphanum, musculis lateralibus 



elongatis. 

 Caput anticum, absconditum. 



Tentacula cervicalia, numerosa, elongata, subcapitata, apicibus suctoriis ? 

 Pallium tumidum, plicatum, pedis basin cingens. 

 Branchice duo, pectiniformes, abdominales ? 

 Pes terminalis, magnus, extensus, subcylindricus, subattenuatus, vermiformis, 



VOL. XVII. F 



