646 



W. D. SMITH 



TABLE I* 



S. nodosus var. brevis 



From these figures we see that the protoconch is wider than the 

 first coil, and consequently must bulge beyond it (see also Number 15, 

 Fig. 1). The first few whorls, up to the third, are slender, and the 

 umbilicus is correspondingly wider proportionally than in the case 

 of the mature form. The involution in the larval and adolescent 

 stages remains fairly constant, about 1 : 3, i. e., embraced part of 

 the coil to the exposed portion; while in the adult it is 1 : 4 and 1 : 5, 

 becoming less and less until in the old or senile stage the involution 

 becomes negative, i. e., the outer coil begins to leave the inner coil. 

 In both the Pacific province forms and those from the interior an 

 impressed zone at the end of the last body chamber can be seen, 

 which shows clearly that these animals were once coiled throughout, 

 not these particular individuals, but the earlier members of the group. 



At the beginning of the adolescent stage the following are the 

 measurements : 



Diameter of shell 

 Height of whorl - 

 Width of whorl 

 Involution 



2.26 



0.76 

 0.84 

 0.12 



The shell at this stage is absolutely devoid of any marked sculp- 

 turing, save the presence of very fine lines of growth running around 

 the coil, parallel to the outline of the aperture. The sutures con- 

 tinue developing gradually. The first change noticed is the develop- 

 ment of marginals on the siphonal lobe. Then between the siphonal 

 lobe and the first lateral lobe, and likewise between all the principal 

 lobes, develop smaller secondary lobes. Fig. 3, Number 3, shows the 

 suture at a diameter of 4 mm . 



1 VII and IX different individuals. 



