FOSSIL REMAINS. 



6-21 



specimens. They arc imbedded in flint, and are par- 

 ticularly remarkable as exhibiting many of the spines 

 attached, which is a circumstance of very rare occur- 

 rence. 



The fossil coverings or shells of the mollusca arc 

 amongst the most abundant of the organic remains, 

 found in the strata of which this globe is composed. 

 They are not only of great variety of forms, but also 

 differ considerably in magnitude. Some, as the am- 

 monite, occur of several feet in diameter, while others 

 are so small as to require the microscope to develope 

 them. They are divided into univalve, those com- 

 posed of one piece or valve ; bivalve, those having 

 two valves : and multivalve, those with more valves 

 than two. 



The univalves are further subdivided into unilocu- 

 lar, those having but one chamber, of which the com- 

 mon limpet is an example, and those having many 

 chambers, called fiom that circumstance multilocular, 

 which division is well exemplified by the nautilus. 

 Of the unilocnlar, a vast number of genera occur in 

 the fossil state, and many of these include numerous 

 species. The genera of multilocular shells are not so 

 numerous, but their internal structure is of such inte- 

 rest as to deserve more particular notice. We may 

 take the nautilus as our example, as being the best 

 known of them ; this has its shell formed into a num- 

 ber of chambers, each separated from the other by a 

 division which is perforated with a small hole. The 

 inhabitant is one of the sepia or cuttle-fish tribe, and 

 resides in the upper or last formed chamber, which is 

 consequently the largest. A tube, which is elastic, 

 and to which the name of siphunculus has been 

 given, proceeds from the animal, and, passing through 

 the perforations in the divisions and the different 

 chambers, terminates in the first or smallest one. It 

 is conjectured, that a portion of the shell is contained 

 within the body of the animal, independent of the 

 connection it has with it by means of the siphunculus, 

 which is membranous, and it appears probable is 

 capable- of rendering the animal buoyant or otherwise 

 at pleasure, as the air-bladder does in fishes, by its 

 being dilatable or compressible as occasion may re- 

 quire. The cells or chambers appear to contain 

 nothing but air, as the animal must leave the last one 

 formed as it produces a new one, having no other 

 communication than that which is kept up by means 

 of the siphunculus. Thus the animal, as it increases 

 in size, occupies a new chamber, which is the last in 

 order ; and in like manner all those preceding have 

 been left empty, so that the gravity of the shell can- 

 not be much greater than that of the water of the sea, 

 and hence the addition of a small quantity of air by 

 means of the siphunculus will render it buoyant, and 

 the expulsion or the air, and possibly the addition of a 

 small quantity of water, will cause it to sink. Of these 

 multilocular shells some few, as the nautilus, are found 

 living at the present time, although but rarely met 

 with, while the fossil species are extremely numerous. 

 From this circumstance a question has arisen as to 

 the cause of the great disproportion between the 

 iccent and fossil shells of this family; some maintain 

 that the genera now found fossil are absolutely extinct, 

 while others contend that they arc deep water shells, 

 and may still exist at the bottom of the sea, far beyond 

 the reach of our observation. The structure of these 

 shells, however, as before explained, being so admira- 

 bly and beautifully adapted to render them buoyant or 

 the contrary at the pleasure of the animal, must be 



admitted as a proof that so far from being confined of 

 necessity at the bottom of the sea, they must (sup- 

 posing them still to exist) be able occasionally to rise 

 up to and remain for a time at the surface, and conse- 

 quently would in every probability be met with ; but 

 as hitherto not a single instance of any of these extinct 

 genera having been thus seen is recorded, we may 

 reasonably doubt of their existence at the present 

 time. 



Of this family of shells the ammonites form a re- 

 markable tribe, not only on account of their beauty 

 and variety, but also for their vast abundance and 

 wide distribution in the mineral kingdom. By the 

 vulgar they are supposed to be petrified serpents, and 

 by others are considered as the types of the volutes 

 of the Ionic order. In India they are regarded with 

 great reverence by the Hindoos, as the emblem of 

 one of their divinities. They occur in the gault, 

 where their colours and pearly lustre are frequently 

 most beautifully preserved. They are exceedingly 

 abundant in the oolite and lias ; upwards of 300 spe- 

 cies have been described. 



Our limits will not allow any further details respect- 

 ing the remaining members of this family. Of these 

 the BELEMNITE has already been described under 

 that head, one of the species of which appears in the 

 plate of FOSSIL REMAINS ; another of these curious 

 fossils, the harnite, is also figured. These as well as 

 the nummulites, orthoceralites, &c., all agree in their 

 general character and economy with the nautilus 

 already particularly described. 



'Of the bivalve fossil shells the specimens are so 

 numerous and varied in their forms, that it would be 

 absolutely impossible to notice them in a single arti- 

 cle. The reader must, therefore, be referred for an 

 account of them either to their several descriptions 

 in this work, under their respective names, or to the 

 numerous treatises and works on fossil conchology. 

 The multivalves are, comparatively speaking, of but 

 rare occurrence. 



From the perishable nature of insects, animals of 

 this class rarely occur in a fossil state. They are, how- 

 ever, found in considerable abundance, and in ex- 

 cellent preservation, in a fresh water deposit at Aix in 

 Provence. They are there so well preserved that their 

 genera, and even their species, may be determined ; 

 sixty-two are enumerated by M. Marcel de Serres as 

 belonging chiefly to the orders Diptera, Hcmiptera, 

 and Cokoptera. Mr. Curtis observes, on reviewing a 

 collection from Aix, that they are all of European 

 forms, and to be referred to existing genera. But 

 one was found to be aquatic. " The antennse, tarsi, 

 and trophi, are generally very obscure or distorted ; 

 in a few the claws are visible, and the sculpture and 

 even some degree of local colouring are preserved ; 

 the nerves of the wings in almost all the diptera are 

 perfectly distinct, and even the pubescence on the 

 head of one of them. Several of the beetles have 

 the wings extended beyond the elytra, as if they had 

 made an effort to escape by flying, or had fallen into 

 the water while on the wing." 



Many species of crabs occur in a fossil state. They 

 are found in the Stonesfield strata and in the limestone 

 at Pappenheim. They are also extremely abundant 

 in the blue clay of the Isle of Sheppy, and many 

 remains of crustaceous animals also occur in the 

 chalk. But the most singular of these crustaceous 

 remains is a fossil which was first observed about a 

 century ago in the Dudley limestone. It attracted 



