205 
cess was sometimes performed with that which Mr. Home has here 
shown takes place in the shell of the toredo, and by which the size of 
the immediate residence of the animal is adapted to the size of the ani- 
mal itself. But since the publication of the first volume, I have had 
the opportunity of ascertaining, that this concameration of the shell of 
the teredo occurs so closely, and with so much regularity, in some 
specimens, as to give reason for believing that it may become the cha- 
racter of a species. A specimen of this kind, in a piece of wood from 
Southend, Essex, is represented Plate XIV. Fig. 11 ; and I know that 
among the specimens of the British Museum, is a much larger speci- 
men, possessing the same character. 
A Veronese fossil in my collection is rendered deserving of notice by 
the very close resemblance which it bears to T.giganlea,m the markings 
and in the stalactitic appearance of its surface : it is about an inch and 
a half in diameter. Plate VII. Fig. 9, is a small fossil of a curious 
structure, the single tube bifurcating, and bearing somewhat, in minia- 
ture, of the appearance which is exhibited by the large teredo figured 
by Rumphius, in which two long tubes proceed from the exterior one. 
The next subdivision of fossil bivalves, which requires our attention, 
is that which comprises inequivalved and irregularly formed shells. 
CXXX. Diceras. A ventricose, transversely subrugose bivalve : 
the beaks distant, shaped like horns, and contorted in irregular spires. 
The valves of this fossil shell are unequal, tuberous and conical, and 
somewhat resemble two cornucopia:, turned spirally but irregularly, 
with their openings applied together. In the larger valve is the hinge- 
tooth, obtusely conical and very large and thick, resembling an ear with 
its cavity. This tooth is articulated, with a corresponding tooth in the 
other valve. Two lateral muscular impressions seem to point out its 
greater degree of relationship to the chamae than to any other shells. 
This curious fossil was found by M.Saussure, in the mountain Saleve, 
in a calcareous stratum, Voyage dans lesAlpes, Tome i. p. 190, PI. n. 
Fig. 1 . a 4. It was also found by M . de Luc, at about one third of the height 
of the mountain. But one species of this shell is known, D. arietina. 
