828 CLASS xin. 



Baculites LAM. Shell straight, conical. 



Sp. Baculites Faujasii LAM., FAUJAS DE ST FOND Hist. not. de la mont dc 

 St Pierre, PI. 21, figs, 2, 3. QUENSTEDT unites with this Baculites anceps 

 LAM. and Baculites vertebralis BRONN, Leth. yeogn. Tab. xxxm. fig. 6. 

 These and Baculites neocomiensis D'ORB. are species from the chalk-for- 

 mations, Baculites acuarius QUENSTEDT, Tab. 21, fig. 15,13 hitherto the only 

 known species from the /wra-formation. 



B. Dibranchiata. 



In this division of Cephalopods, to which most of the species now 

 living belong, the funnel is closed below. There is an organ for the 

 secretion of a black fluid, which the animal can eject through the fun- 

 nel, the ink- sac. In the genus Octopus this ink-sac is enclosed within 

 the liver } but in the rest is remote from it. The colouring matter of 

 some species is used as a paint, Sepia. Since some observations have 

 indicated the presence of an ink-sac in the fossil Belemnites l , it may 

 probably be concluded, with OWEN, that these petrifactions are in- 

 ternal shells of Cephalopoda dibranchiata, which conclusion has, in 

 fact, been since established by the observation of petrified animals 2 . 



Family XIII. Decacera s. Sepiacea. Arms ten, two longer 

 than the rest, round. 



Belemnites BREYN, LAM. Shell fossil, conical, including inter- 

 nally a multilocular, shorter portion (alveolites) . 



Belemnites or dart-stones; thus named on account of their dart- like form. 

 These petrifactions are found abundantly in the secondary mountains of 

 the oolite and chalk-periods. Compare, amongst others, DUCROTAY DE 

 BLAINVILLE Mem. sur les Belemnites, Paris, 1827, 4to; J. S. MILLER 

 Observations on Belemn., Transact, of the Geol. Soc. of London, sec. Series, 

 n. 1829, pp. 43 62, PI. 6 9; BRONN Leth. geogn. pp. 402 418, pp. 

 714720. 



Spirula LAM. Animal with ten tentacles, two longer. Shell 

 placed in the posterior part of animal, thin, spiral, with wreaths 

 not contiguous. Partitions concave, perforated by siphon at the 

 inside. 



1 AGASSIZ in V. LEONHARD u. BRONN News Jahrb. fur Mineralogie, Geognosie u. 

 Geol. 1835, s. 163, BDCKLAND Geology and Mineralogy, London, 1836, 8vo, (Bridge- 

 water Treatises, vi.) p. 374, PI. 44', fig. 7, PI. 44 ". 



2 Lectures on the comp. Anat. and Physiol. of invertebrate Animals, p. 337, 2nd ed. 

 PP. 597603. 



