96 



MOLLUSCA. 



The nautilus spirula of Linnaeus has afforded characters 

 for the construction of a new genus termed SPIRULA. The 

 whorls are separate, the mouth orbicular, the partitions per- 

 forated by a tube, and the last turn of the spire prolonged 

 in a straight line. This last character was unknown to Lin- 

 naeus, who had only seen the spiral body of the shell. 



The genus SPIROLINA has the last turn of the spire pro- 

 duced like the preceding, but the whorls are contiguous. 

 The partitions are perforated by a tube. 



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 AMMO- 

 NITES, including those shells which have been termed cor- 

 nua ammonis. The origin of this name is, by some, sought 

 for in their resemblance to the horns of a ram ; by others, 

 to their having been found near the temple of Jupiter Am- 

 mon 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 peebles of the Gandica where it joins the Gan- 

 ges. In this genus the whorls are contiguous, spiral, de- 

 pressed, and obvious. ' 



The ORBULITES of Lamark differs from the ammonites 

 in the circumstance of the last whorl embracing and con- 

 cealing the others. In both the syphon is marginal. 



Nearly allied to the preceding is the TURRXLITES of 

 Montfort. It is similar in internal structure, but while the 

 shells of the former are spirally discoid, those of the present 



