mille trés-naturelle, qui avoisine celle des Canaliferés 
par ses rapports, mais qui en est éminemment distincte.”’ 
This able classifier (whose perception of affinities is truly 
admirable), then proceeds to divide these shells into three 
groups, founded upon such excellent distinctions, that we 
need not here dilate on their importance. Two of these 
genera are characterized by a deep and well defined sinus 
or notch, towards the base of the outer lip; quite distinct 
from the basal canal, and intended either for the passage of 
the animal’s proboscis, or its respitory siphon. In Strom- 
bus the outer lip is dilated, but entire; in Pteroceras, it is 
equally enlarged, but divided into long processes. Such 
are the typical distinctions, and their immediate union 
appears effected by the Strombus laciniatus of Chemnitz. 
The third genus of Lamarck’s is Rostellaria, in which he 
places all those species wherein the sinus above mentioned 
is united to the basal canal. Now if the Strombus pes- 
pelecani of authors had this canal more closed, and the 
sinus distinct, it would be a Pteroceras. Da Costa long 
ago placed this shell as the type of a genus, and the obser- 
vations of Mr. Dillwyn, in his short but highly valuable 
paper on fossil shells (Phil. Trans. for 1823, p. 1, p. 393), 
have shewed the importance which we should attach to its 
structure: it is, in fact, a Pteroceras, but with the above 
mentioned sinus removed to the base of the digitated lip, 
and confounded, as it were, with the basal canal. Excepting 
to a Pteroceras, it cannot be compared with any known 
shell, unless it be to the Strombus fissus of Linn. The 
hiatus between them certainly appears great, yet the affinity 
is not interrupted by any thing known: this latter shell 
resembles the true Rostellarix, but with the digitated pro- 
cesses of Pteroceras reduced to teeth; which teeth, in 
R. curvirostris, become confined to the basal part of the 
unexpanded lip. We are here met by certain fossil shells, 
preserving the form of Rostellaria, but with the outer lip 
entire, and sometimes considerably expanded: in these 
the spiral canal sometimes extends to the summit of the 
shell: finally the distinct sinus again appears in such spe- 
cies as S. cancellatus, canalus, &c., all which have been 
classed by conchologists with Strombus. This series is 
sufficient to shew the tendency of a circular disposition of 
relations, but very many of the intermediate forms are 
wanting, nor is it at all clear in what way the immediate 
passage is effected between Hippochrenes and the genuine 
Strombii. 
