81 
as of the genus Certithium, are frequently seen in the Portland free- 
stone. Shells of this genus are also frequent among the Veronese 
and Vincentine fossils. 
Lamarck enumerates ten species among the fossils of Grignon, 
Chaumont, &c. : T. imbricataria, T. sulcata , T. subcarinata, T.fasciata, 
T. multisulcata, T. terebellata , T. perforata , T. unisulcata , T. uniangu- 
laris, T. melanoides. 
XLIV. Pupa. A somewhat cylindrical univalve ; the last turn of 
the spire, which is somewhat produced, not being larger than the 
preceding : the aperture irregularly roundish or oval ; the margin 
continued circularly. 
Turbo uva, Linn. Born. Vign. Fig. e. is the type of this genus, 
which does not appear to be known fossil. 
XLV. Janthina. A subglobose diaphanous univalve : the opening 
triangular, with an angular sinus on the right edge. 
Helix janthina, Linn. List. Tab. 5f2, Fig. 24, is of this genus ; no 
shell of which has, I believe, been found fossil. 
XLVI. Bulla. An ovate, gibbous, and somewhat cylindrical uni- 
valve : the spire not standing out, but concealed within : the opening 
the length of the shell : the lip acute.. 
Bulla aperta, Linn, and Bulla lignaria, Linn, are contained within 
the membranous part of the molluscae by which they are produced, so 
that these molluscae appear naked, or without any external shell ; but 
the lively colours, and the repeated convolutions of other species, as 
Bulla ampulla, Linn. &c. show that these have not been contained 
within the soft part of the animal. Lamarck, apprized of this cir- 
cumstance, has separated the former animals from the genus Bulla, 
and has formed with them a genus of the naked molluscae, and named 
it Bullcea, leaving in the genus Bulla those species, the shells of 
which, possessing the above-recited generic characters, form the ex- 
ternal covering to the animal. 
I do not know of any English fossil shells of this genus. Respect- 
VOL. III. lyr 
