205 



eess was sometimes performed with that which Mr. Home ha& here 

 shown takes place in the shell of the teredo, 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, 1 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 spe- 

 cimens, as to give reason for believing that it may become the character 

 qf a species. A specimen of this kind, in a piece of wood from South- 

 end, Essex, is represented Plate XIV. Fig, 11 ; and I know that, among 

 the specimens of the British Museum, is a much larger specimen, pos- 

 sessing the same character. 



A Veronese fossil in my collection is rendered deserving of notice by 

 the very close resemblance which it bears to T. gigantca, in the markings 

 and in the stalactitic appearance of its surface: it is about an inch and 

 a half in diameter. Plate XIV. 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 cornucopias, 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 chama3 than to any other shells. 



This curious fossil was found by M. Saussure, in the mountain Saleve, 

 in a calcareous stratum, Voyage dans ies Alpcs, Tome i. p. 190, PL u. 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. 



