460 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
21), we see that they have the same curves when looked at one from 
a ventral, the other from the dorsal side; in other words, they are 
mirror images of each another. This reversal of symmetry may 
extend even to the recess; thus in figures 21 (pi. 46) and 33 (pi. 47) 
the recess is on the animal’s right and the orifice of these annuli on 
the animal’s left, but in figure 23 (pi. 46) which is the rare form of 
symmetry, the recess though nearly median was more on the animal’s 
left in this case where the orifice was on the animal’s right. However, 
as in C. affinis the position of the recess is probably too variable to be 
safely brought into consideration of right- and left-handedness. There 
are also marked individual differences in all parts of the annulus, 
in the size and position of the various parts of the trumpet, in the 
angles and lengths of the lines of the zigzag, in the amount of depres¬ 
sion of the ventral surface, and in the amount of elevation of the 
cushions. 
In comparing the right- and left-handedness of C. affinis and C. 
virilis it is to be noted that most of the former had the orifice of the 
trumpet on the animal’s right side while most of the latter had it on 
the animal’s left side. Should an examination of a very large number 
of individuals show that one species is predominatingly right- and 
the other left-handed, it would be interesting to ascertain what rela¬ 
tion this bears to the assumed homology suggested above between the 
posterior three lines of the suture of one species and those of the other. 
That is to say, if the posterior part of the zigzag in each species be 
fixed and the great length of the suture in C. virilis be regarded as 
obtained by an anterior addition of three lines to the three alone 
present in C. affinis , then the position of the third angle in C. virilis 
would be the homologue of the orifice in C. affinis. The two tuber¬ 
osities in the latter species would be imagined as reduced to the two 
ridges right and left of this third angle in C. virilis. As this third 
angle in C. virilis is on the right (pi. 46, fig. 21; pi. 47, fig. 29) when 
the orifice is on the left of the animal and on the left when the orifice 
is on the right (fig. 23, pi. 46, s udied with fig. 31, pi. 47), in other 
words, since the third angle is on the side opposite to the orifice, it fol¬ 
lows that if the angle be homologous with the orifice of C. affinis then 
the orifice of C. virilis is a new one on the opposite side. Thus the 
prevalence of left-handed orifices in C. virilis would be deduced from 
the prevalence of right-handed orifices in C. affinis and both species 
would agree in having right-handed annuli as the prevalent form so 
far as the fundamental posterior parts were concerned. 
