Clifton College Scientific Societ//. 75 



of a membrane, covered externally with many hundred angular 

 calcareous plates of minute size. At the apex of this funnel was 

 an aperture forming the mouth, which extended like a proboscis 

 when required to receive food ; this is situated in the centre, sur- 

 rounded by the arms. The body is small ; the arms and fingers 

 long and spreading, furnished with numerous tentacula ; each 

 joint is armed at its margin with a small tubercle acting as an 

 organ of prehension, but the form of it varies in almost every 

 joint ; these arms, with all their apparatus when expanded, must 

 have formed a net of much greater activity than even the encrinite. 

 We have seen that the bones of the encrinite exceed 26,000 ; those 

 in the fingers and tentacles of Briareus must amount to at least 

 100,000, to which must be added 50,000 ossicula of the side arms 

 (and the number is probably really far greater) ; thus the total 

 number will exceed 150,000 bones, to each of which were attached 

 two fasciculi of fibres, which served as muscles. 



But, as we have already seen, the shells constitute by far the 

 greater portion of the fossils. The weatherstones, where they 

 chiefly abound, must have been the deposit of shallow seas, 

 where the bodies were subjected to continual trituration. This 

 accomits for the poor state of preservation in which the 

 ammonites and other shells of delicate structure are found. 

 These ammonites can only be drifted specimens, as they usually 

 inhabited deep seas ; therefore, where ammonites are found in 

 any profusion, the beds are thick, and, as a rule, the shells are 

 well preserved. These cephalopods are nearly allied to the 

 nautili, but the place and use of the shell has puzzled many 

 naturalists. Cuvier himself, judging from the small size of the 

 outer chamber where the animal lived, supposed that they were 

 internal shells. He probably came to that conclusion from having 

 seen only imperfect specimens. The outer chamber is seldom 

 preserved entire, but when it is, we find that it bears quite as large 

 a proportion to the rest of the shell as that of the nantihis bears 

 to the chambered interior of that shell. The shells had to serve 

 for protection and as floats, and consequently they are but thin, 

 to admit easy rising to the surface. Their shape is one continuous 

 arch, coiled spirally round itself, so that the base of the outer 

 whorls rest upon the crown of the inner, and thus the keel or 

 back is capable of resisting great pressure. Moreover, the shell 

 is further strengthened by ribs or transverse arches, which give 

 many species their characteristic features. Another source of 

 strength is the elevation, in some species of ammonites, of parts 

 of the ribs into dome-shaped tubercles, by which the power of the 

 simple arch is greatly increased. The foliated transverse plates were 

 added doubtless for the same purpo.se. The most important organ 



