276 BACULITE. 



bered shells, called Lituites. (PI. 44, Fig. 3.) These are 

 partially coiled up into a spiral form at their smaller ex- 

 tremity, whilst their larger end is continued into a straight 

 tube, of considerable length, separated by transverse plates, 

 concave outwards, and perforated by a siphuncle (a.) As 

 these Lituites closely resemble the shell of the recent Spirula 

 (PI. 44, Fig. 2,) their office may have been the same, in the 

 economy of some extinct Cephalopod. 



Baculite. 



As in rocks of the Transition series, the form of a straight 

 Nautilus is presented by the genus Orthoceratite, so we find 

 in the Cretaceous formation alone, the remains of a genus 

 which may be considered as a straight Ammonite. (See 

 PI. 44, Fig. 5.) 



The bacuUte (so called from its resemblance to a straight 

 staff) is a conical elongated, and symmetrical shell, de- 

 pressed laterally, and divided into numerous chambers by 

 transverse plates, hke those in the Ammonite, are sinuous, 

 and terminated by foliated dentations at their junction with 

 the external shell ; being thus separated into dorsal, ventral, 

 and lateral lobes and saddles, analogous to those of Ammo- 

 nites.* 



It is curious, that this straight modification of the form 

 of Ammonites should not have appeared, until this Family 

 had arrived at the last stage of the Secondary deposites, 

 throughout which it had occupied so large an extent ; and 

 that, after a comparatively short duration, the Baculite 



• The externa! chamber (a) is larger than the rest, and swelling ; and ca- 

 pable of containing a considerable portion of the animal. The outer shell 

 was thin, and strengthened, like the Ammonite, by oblique ribs. Near the 

 posterior margin of the shell, the transverse plates are pierced by a Sipiiuncle 

 (PI. 44, S"*, c.) This position of tiie Siphuncle, and the sinuous form and 

 denticulated edges of the transverse plates, are characters which the Bacu- 

 lite possesses in common with the Ammonite. 



