ORYCTOLOGY. 



even to a very fine powder, leaving in 

 some instances a stony, correctly mould- 

 ed, cast of the cavity of the shell ; that 

 verv frequently the substance of the shell 

 is entirely altered, having 1 become a cal- 

 careous stone, or a silicious or pyritous 

 mass, and that the shells of a former 

 world are frequently found in masses of 

 marble, which is called lumachelli, or 

 shelly marble. 



Of the JVIulti valves, ihe chiton does not 

 appear to have been found in a mineral- 

 ized state ; and although several species 

 of Lepas have been found in a mineral 

 state, they are by no means frequent fos- 

 sils. Lepas anserifera is said to have 

 been found fossil, as well as Lepas diade- 

 ma ; these must, however, be exceeding- 

 ly rare fossils. 



Fossil shells of the Pholas are by no 

 means common ; the Pholas crispata has 

 been, however, found among the Harwich 

 fossils. 



Fossil bivalves are very common fossils; 

 they are, as might be expected, very sel- 

 dom found in pairs, except, when united 

 by a lapideous mass, which prevents the 

 examination of their hinge, or their inter- 

 nal structure, which in many fossil shells 

 are objects highly worthy of examina- 

 tion. 



The Mya pictorum is described by So- 

 Jander as existing among our Hampshire 

 fossils : a fossil mya of three or four inches 

 in length, is found also in the rocks near 

 Bognor. Remains of the solen siliqua, 

 and of the solen ensis, have been found 

 at Harwich, and a small fossil shell, nam- 

 ed by Solander solen ficus, has been 

 found between Lymington and Christ- 

 church. 



Fossil shells of the genus Tellina, as 

 well as of cardium, mactra, donax, venus, 

 sponclylus, chama, area, and particularly 

 ostrea, have been found of many spe- 

 cies. But no bivalve exists as a fossil in 

 such prodigious numbers, and in such 

 various species, as those of the genus 

 Anomia. These shells are characterized 

 by the beak of the largest or under valve, 

 which is perforated, being greatly pro- 

 duced, rising or curving over the beak 

 of the smaller or upper valve. Anomia 

 lacunosa (Plate II. fig. 1.) is one of the 

 most abundant of these species. They 

 are found in considerable quantities in 

 different parts of England, particularly 

 in Lincolnshire, Warwickshire, and Glou- 

 cestershire. Anomia terebratula, (Plate 

 II. fig. 2), is another fossil of this genus, 

 which exists in different counties in this 

 island, in great abundance. 



Of the genus Mytilus several species 

 are known as fossils, some; of which ap- 

 proach very near to those which are 

 known recent: one in particular appears 

 to differ very little indeed iix-m .Mytilus 

 modiolus. Fossil shells of the genus 

 Pinna, in any tolerable preservation, are 

 not frequently found : the shells are in 

 general so fragile as to render it very 

 difficult to obtain them tolerably perfect ; 

 or so that but litile information can br 

 yielded respecting the species to which 

 they belong. 



No fossil shell appears yet to have 

 been found which can with certainty be 

 placed under the genus Argonauta. But 

 of the genus Nautilus, specimens are 

 very frequent. These have been found 

 in several parts of this island : some very- 

 tine specimens have been found at Lime 

 in Dorsetshire, in different parts of Wilt- 

 shire, and at Wliitiby in Yorkshire. The 

 finest specimens are perhaps found in 

 the neighbourhood of iJuth, and in the 

 Isle of Sheppey in Kent, at whirii hitter 

 place they are found exceedingly large, 

 and still retaining a resplendent pearly 

 shell. (Plate IT. %. 3.) 



The Cornu Ammnnis, which, if we ex- 

 cept the extremely minute shells of this 

 kind which have been setn by Plancus, 

 and others, in the sea sand on the Vene- 

 tian shores, may be said to be only known 

 to us in a fossil btate 



Like the Nautilus, the Cornu Ammonis 

 is divided into compartments, by regular- 

 ly disposed partitions, and these parti- 

 tions are perforated, as are those of the 

 Nautilus, although it is by no means easy 

 to point this out, except in very few spe"- 

 cimens. 



There are none of the fossil shells, ex- 

 cept perhaps the Anomia;, which can vie 

 in the variety of their species with the 

 Cornu Ammonis. The shell of some is 

 perfectly smooth over its whole surface; 

 in others smooth at the sides, but ridged* 

 or beset with spines at the back ; and 

 others, though smooth at the side, are cre- 

 nulated at the back. The species most 

 commonly met with have the shell vari- 

 ously ridged ; some wiih small close strire, 

 and others with large and round ridges. 

 In some the ridges are single, in others 

 bifurcated, and in others triiurcated. In 

 some, and these are least common, the 

 shell is tuberculated : these tubtrculze 

 differing considerable in different species, 

 in their size, form, and disposition. The 

 different species proceeding from the in. 

 '.ci-mixture of ail these varieties, it must 



