PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. XXI 



a prominent place in the earlier formations was occupied by that 

 group which presents the least development of the distinctive cha- 

 racter of the cephalopod class, and which has much in common with 

 the testaceous Gasteropods. . . . The paucity of remains of typical 

 Gasteropods, at the same period .... remarkable ; and some of 

 those forms which are most abundant (e. g. Euomphalus and Belle- 

 rophon) present indications of close affinity to Cephalopods. So that 

 it would seem as if the Nautiloid type is really to be regarded as 

 having occupied the place at that period, not merely of the order 

 above [fishes], but also (in part) of the order below ; its decline and 

 almost complete disappearance during the Secondary epoch, being 

 coincident with the multiplication of the forms of more typical Gas- 

 teropods and of the higher Cephalopods." 



Professor Owen divides the Tetrabranchiata into Nautilidse and 

 Ammonitidse. The fossils already spoken of are of the Nautilidse, 

 and sufficient authority has been adduced to show that they are the 

 lower of the two families. The higher family of Ammonitidse does 

 not make its appearance till the Lias. There are, however, inter- 

 mediate forms. In the Devonian formation occurs Clymenia, which 

 forms a link with the Goniatite of the mountain limestone, a fossil 

 approximating, if not fully belonging to the Ammonite family. The 

 distinction^ are chiefly in the form of the septa or walls which divide 

 the chambers of the shells. A living palaeontologist says " As we 

 ascend in the Palaeozoic series, we find that various of the primitive 

 genera and species disappear, and are succeeded by other forms, dis- 

 tinct from, but closely allied to them ; which, in their turn, are lost." 

 Edwards : Monograph of Eocene Mollusca. 



" On passing into the Mesozoic (secondary) series, a marked change 

 takes place. Of the eight genera constituting the family of the 

 Nautilidae which lived during the Palaeozoic epoch, Orthoceras and 

 Nautilus alone survive ; and of the long series of species belonging to 

 the latter genus, whose remains are found in the carboniferous forma- 

 tions, every one disappears ; but an immense array of Ammonites 

 starts into existence, with septa at first comparatively simple, but 

 becoming more complicated in structure in the succeeding forma- 

 tions." Edwards. 



We now come to the Dibranchiate Cephalopods. Professor Owen 

 divides them into two tribes, the Decapoda, which, besides eight 

 sessile arms round the mouth, have two tentacula placed one on each 

 side, and the Octopoda, which have the eight arms, but want the 

 two tentacula. He places the former lowest. " The Decapodous 

 tribe," he says, " is that which is most nearly allied to the Tetra- 

 branchiate order. This affinity is not only indicated by the addi- 

 tional number of external arms, and the frequent development of an 

 internal circular series of eight short labial tentacles, but by several 

 internal characters ; as the single oviduct and detached glands for 

 secreting the nidimentum ; the valve of the funnel ; the laminated 

 rudiment of a chambered shell in the Cuttle-fish, and the fully deve- 

 loped chambered and siphoniferous shell of the Belemuites and 



