432 f'HII-OSOPHY OF ZOOLOGY. 



1, Head s^urrounded with eight arms and two feet. 



The two feet are nearly similar in their structure to the 

 arms, or tentaeula, but considerably larger in their dimen- 

 sions. They have their origin on the ventral side of the 



The genus Discorbis of Lamark (formerly called by him Planulites), 

 bears a considerable resemblance to the Nautilus in form, but the whorls are 

 all apparent, and the partitions entire. The following species of the genus 

 Nautilus of Montagu, may be inserted in this genus, viz. crassulus^ infiu' 

 tu8, carinatulus, Beccarii and Beccarii pervtrsus. Were we acquainted with 

 the position of this last shell in the animal, we might, on account of its si- 

 nistral whorls, consider it as belonging to a new genus. 



In the genus Rotalia, the spires approach to a conical shape, and the mar- 

 ginated trigonal aperture is reflected towards the base of the shell. It con- 

 sists of shells which are now found in a fossil state. 



The Nautilus spirula of Linnsos has afforded characters for the construe- 

 tion of a new genus termed Spirula. The whorls are separate, the mouth 

 orbicular, the partitions perforated by a tube, and the last turn of the spire 

 prolonged to a straight line. This last character was unknown to Linm^us, 

 who had only seen the spiral body of the shell. 



The genus Spirolina has the last turn of the spire produced like the pre- 

 ceding, but the whorls are contiguous. The partitions are perforated by a 

 tube. The Nautilus semilttnus and subarcuatulus of Montagu are of this 

 genus. 



The genus Lituola is allied to the spirula and spirolina in the production 

 of the last whorl. The spires of the body are contiguous, and the partitions 

 are pierced by a number of holes. 



In the preceding genera the inner walls of the cavity are simple ; but in 

 the two following, the walls are formed into joints by sinuous sutures. The 

 first of these is the Ammonites, including those shells which have been 

 termed cornua ammonis. The origin of this name is sought for in their 

 resemblance to the horns of a ram, and to their having been found near 

 the temple of Jupiter Ammon, in Upper Egypt. By the Indians, the 

 Ammonites sacer is considered as a metamorphosis of the god Vishnu, and 

 termed by them salgram or salgraman. It is found among the pebbles of 

 the Gandica, where it joins the Ganges. In this genus the whorls are con- 

 tiguous, spiral, depressed, and obvious. 



The Orbulites of Lamark difTers from tlie Ammon'tes in the circuni- 

 etance of the last whorl embracing and concealing the others. In both the 



