3308 



THE MOLLUSKS OR SHELLFISH 



A CERATITE (Ceratites nodosus). 



Allied Families 



habits and economy of the pearly nautilus, but, as already remarked, it is most 

 likely a deep-water animal, as a rule living at depths far beyond the action of 

 storms. It would probably be obtained by dredging or by means of baited traps. 

 A specimen dredged off the Fiji islands, at a depth of about three hundred and 

 twenty fathoms, was kept alive for some time in a tub of sea water. The mode 

 of growth of the nautilus has been a subject of much discussion, and the way in 



which the successive air chambers and septa 

 are formed is not known with certainty. 

 The living forms of Nautilus probably belong 

 to three distinct species. N. pompilius has a 

 a wide distribution in eastern seas, specimens 

 having been obtained in the Indian Ocean 

 (Andaman islands), at the Moluccas and 

 Java, and in the Pacific at the New Hebrides 

 and Fiji; N. umbilicatus is recorded from the 

 Solomon islands and New Ireland; and A^ 

 macromphalus from New Caledonia and the 

 Isle of Pines. The animal of Nautilus is used 

 as an article of food among the natives of the 



New Hebrides, New Caledonia, and Fiji, it being captured by the Fijians in traps 

 baited with boiled crawfish. 



The genus Nautilus is of great antiquity, dating from an early 

 epoch in the Paleozoic period, and forms the type of the famity Nau- 

 tilidce, which includes several extinct genera. There are allied extinct families, col- 

 lectively forming a group characterized by the simple structure of the septa of the 

 shell, such septa having their concavities directed toward its aperture. Among 

 these, the Orthoceratidce , as typified by the Paleozoic genus 

 Orthoceras, may be characterized as unrolled nautili, the 

 shell which sometimes reaches an immense length 

 forming a long cone. 



Another well-marked group is that of the Ammonoidea, 

 represented by the goniatites of the Paleozoic, and the 

 various types of ammonites of the Secondary rocks, as well 

 as by the turrilites of the Chalk. In all these the edges 

 of the sutures, where they join the shell, are more or less 

 complexly angulated or frilled, the complexity being very 

 great in the ammonites, but a simpler type obtaining in the 

 gouiatites. Whereas in the two latter the shell is coiled in 

 a flat spiral, in the turrilites it forms a cone, while in the 



hamites and baculites of the Chalk it is either straight or partially coiled. In the 

 ceratites and ammonites (which include Ceratites, Cardioceras, and many other 

 genera) the mouth of the body chamber of the shell was closed by an operculum, 

 which often consists of two pieces meeting in the middle line, and the whole being 

 heartshaped. In other forms the operculum was single. Mr. Cooke observes that 

 "some authorities hold that the members of this suborder belong to the Dib- 



AN AMMONITE 



( Cardioceras cordatum) . 



