570 DESCRIPTIONS OF SOME NEW SPECIES OF PULMONATE MOLLUSCA. 



I have to apologise for the illustrations I offer of this shell, 

 which are far from good, and should be interpreted with the 

 corrections conveyed in the description. The outline, fig. 10, 

 represents the shell of the natural size ; fig. 5 is magnified three, 

 and figs. 2 and 8 six diameters, respectively. 



The large central figure on PI. xx., fig. 1, is the animal of 

 Bulimus MacConnelli, Reeve. 



Fig. 9 on PI. xxi. is a very faithful representation of the animal 

 of Coeliaxis australis, Forbes, = Balea australis, Forbes. 



Figs. 4 and 7 are enlarged figures of the young state of Coeliaxis 

 before decollation has occurred. I wish to draw special attention 

 to the enlargement of the second whorl in this stage of develop- 

 ment. I find from observation that it is this enlargement which 

 first shows signs of dissolution and which ends in decollation. 



The carbonate of lime, of which this thickened whorl is com- 

 posed, is more exposed to the carbonic acid held in solution in 

 the clamp localities which this species inhabits, than the other 

 whorls are ; its prominence causes the epidermis to be early worn 

 off it ; being exposed, the carbonic acid in solution more readily 

 acts on the insoluble carbonate of lime composing it, and converts 

 the insoluble carbonate into a soluble bicarbonate. The erosion, 

 as far as I have been able to observe from specimens kept in a 

 box of damp sand, never begins in the apex; the apex really drops 

 off when this nodose second whorl becomes dissolved. What 

 purpose this enlargement of the second whorl serves in the 

 economy of the young is difficult to conjecture ; it may be that 

 its increased weight in the early developmental stage would cause 

 it to lie flat beside the animal, and in this way would be less 

 exposed to injury as the animal glides about ; or it may be for 

 increased strength for protection. 



