391 



As an example of these relations the following Table is given, and 

 it might have been extended and rendered more complete, had the 

 author not preferred to limit it to such cases as have come under his 

 own examination. 



This Table shows the natural affinities of four principal divisions of 

 terrestrial gasteropods, proceeding, as it were, in parallel lines, with- 

 out any very obvious lateral connexions, through fluviatile and littoral 

 forms, conducting to certain marine genera distinguished by this 

 alliance from all others having no terrestrial representatives, and 

 being therefore more restrictedly marine. It may be remarked that 

 the importance of the characters placed at the head of the Table has 

 been proved by the comparison of other anatomical particulars in 

 those genera, and so far their efficiency in other cases is sub- 

 stantiated. 



The author adds the following observations on the anatomy of the 

 Siphonaria and Amphi6ola> as bearing on their position in the first 

 series of the foregoing Table : 



"Siphonaria appears to enjoy the power of breathing in both 

 air and water with equal facility, and on examination, we find the 

 respiratory surface so constituted as to afford a ready explanation of 

 the fact. Thus, in connexion with a narrow, combed, or rather 

 transversely plaited gill, numerous vessels ramify extensively, and 



