14 PROCEEDINGS OF THE ACADEMY OF [Jan., 



the Sturridge specimens. The reduction in size in L. granulosa 

 in these localities is accompanied by a shght reduction in the size 

 of the embryonic- shell or protoconch, which is easily observed 

 in all cases in the adult shell. The minor diameter of the protoconch 

 averages 0.47 mm. in the specimens from the larger group, the 

 average being for the Benmore specimens 0.444 mm., for the Somerset 

 Road specimens 0.47 mm., and for the Somerset specimens 0.50 mm.; 

 as against an average of 0.416 mm. for the Kendal Road specimens 

 and 0.408 for the Sturridge place forms. There is thus a dwarfing 

 that is not alone individual, but a racial dwarfing. These characters 

 are well shown by a comparison of the dimensions by whorls which 

 is given in fig. 2. A series of characteristic specimens were selected 

 from each locality and each individual measured by whorls with an 



^ ' 



Fig. 2. — Lucidella granulosa. Comparison of width and height by whorls. 

 Sm. = Somerset, S. R. =Somerset Road, B. =Benmore, St. = Sturridge, 

 K. R.= Kendal Road. 



eyepiece micrometer on the microscope, using of course a mechanical 

 stage to adjust the specimen. The measurements by whorls and 

 the minor diameter of the protoconch are plotted in the figure. 

 This last character hardly shows well at this scale, the differences 

 being small. The comparison by whorls brings out the fact that 

 in spite of the dwarfed character of two of these races, but little 

 reduction in size is shown up to the third whorl and the difference 

 in size only becomes pronounced at the fourth whorl. All of these 

 forms, whether normal or dwarfed, possess at least five whorls, 

 so that up to this point the growth rate is strictly comparable. 

 The marked falling off in size of the two dwarfed races at this point 

 is to be attributed to the environment alone. The still more marked 

 falling off in diameter as shown in the last whorl is partly due to a 

 reduction in the number of whorls in the dwarfed races, this falling 

 from the maximum of somewhat over six whorls in the larger forms 

 from Somerset, Somerset Road, and Benmore to between five and six 



