CEPHALOPODA. 185 



not exist in very deep water. They were probably limited to 

 a depth of 20 or 30 fathoms at the utmost.* 



It is certain that the sexes were distinct in the tdrabranchiata. 

 M. D'Orbigny, noticing that there were two varieties of almost 

 every kind of ammonite — one compressed, the other inflated 

 — naturally assumed that the first were the shells of male indi- 

 viduals ((?), the second of females (9). Dr. Melville has made 

 a similar suggestion with respect to the nautili ; namely, that 

 the umbilicated specimens are the males, the imperforated shells, 

 females. Professor Van der Hoeven has described the difference 

 in the shells of the two sexes ; f but these are trivial as com- 

 pared with those presented by the animals. The most marked 

 is that while the female has twelve retractile tentacles, the male 

 has only eight, while the other four tentacles are coalesced 

 together to form an organ called the spadix. 



In 1865, M. Barrande published the plates to his second 

 volume on the Cephalopods of Bohemia. We have not been 

 able to see this work : but it contains 107 plates, with figures of 

 200 species of cephalopods, belonging to the genera Ooniatites, 

 Nothoceras, Trochoceras, Bercoceras, Lituites, Fhragmoceras, Oom- 

 j^hoceraSy and Ascoceras. 



Family I. — Natjtilid^. 



Shell. Body-chamher capacious. Aperture simple. Sutures 

 simple. Siphuncle central or internal. (Figs. 50, ^1.) 



Nautilus, Breynius, 1732. 



Shell involute or discoidal, few-whorled. Siphuncle central or 

 eub-central. 



In the recent nautili, the shell is smooth, but in many fossil 

 species it is corrugated, like the patent iron-roofing, so remark- 

 able for its strength and lightness. (Buckland.) See PL II., 

 Fig. 10. 



The umhilicus is small or obsolete in the typical nautili, and 

 the whorls enlarge rapidly. In the palaeozoic species, the 

 whorls increase slowly, and are sometimes scarcely in contact. 

 The last air-cell is frequently shallower in proportion than the 

 rest. 



By deep water, naturalists and dredgers seldom mean more than 25 fathoms, a 

 comparatively small depth, only found near coasts and islands. At 1.00 fathoms the 

 pressure exceeds 2ti51bs. to the square inch. Empty bottles, securely corked, and sunk 

 with weights beyond 100 fathoms, are always crushed. If filled with liquid, tlie cork 

 is djiven in, and the liquid replaced by salt water ; and in dramng the bottle up again 

 [the cork is returned to the neck of the bottle, genfira^y in a reversed position. (3ir F. 

 ] Beaufort.) 



t Annals of Natural History, vol. xix. 1857. 



