420 Mr ANSTED, on A NEW GENUS 



It is also one of those without the very slightest trace of the lobes 

 alluded to by Count JNIiinster. 



(3). E. minutus nob. Plate VIII., Fig. 3. twice the natural size. 

 This very small and pretty species much resembles two of those de- 

 scribed by Count Miinster, except in the size of the siphuncle, but I 

 have thought it better to give a new name, because of the great im- 

 portance of this difference. Waved strise may be observed on some 

 parts of the only specimen I have examined, but they are very minute, 

 and required the aid of the microscope to discover them. 



It remains now that we consider, from analogy with known genera, 

 how far the animal inhabitant of this new genus may have resembled, 

 in its habits or locality, those of other multilocular shells most nearly 

 allied to it. 



What then are those points in the description of the shell that 

 tell most of the history of the animal, and what light is thus thrown 

 on the subject now under consideration ? 



It was the opinion of Von Buch, an opinion strengthened by the 

 later researches of Dr Buckland, that the siphuncle must be considered 

 as an all-important organ in the structure of a multilocular shell. It 

 is true that the position of the tube has generally been considered 

 much more than its magnitude, but the size must not be neglected ; 

 for assuming Dr Buckland's opinion of its use to be true, m%. that 

 the whole mass of the animal and shell has its specific gravity changed 

 by the pericardial fluid passing into the siphuncle, it is quite clear 

 that the larger this tube in proportion to the area of the septa, the- 

 more sudden will be the change of specific gravity, and consequently 

 the greater the facility with which the animal could alter its depth 

 in the water. 



Now in almost all the known species of the family nautilacea, 

 this contrivance is large, well defended, and eminently adapted for 

 resisting external injury, while on the other hand, it is comparatively 

 rare to find a large siphuncle in an ammonite, or any allied genus, 



