26 McMURRICH. [Vot. III. 
cluded in the variations which the species presents. For instance, 
in B. gemmacea, as figured by Gosse (60) and Andres (’83), the 
tubercles do not as a rule all reach the limbus, but only those 
of the primary series. In Figure 2 of Gosse’s Plate IV. the 
arrangement is similar to what occurs in the Bahama specimen, 
so that this difference may be overlooked. Again, in most cases 
it is only the primary tubercles which are lighter in color; but 
Gosse states that “sometimes, however, the quaternary row 
which bounds each primary on each side is also white,” and he 
figures such a condition in Pl. IV., Fig. 3. If one imagines a 
form with the rows of tubercles all reaching the limbus, and 
having not only the primary tubercles, but also the quaternaries 
on either side, light colored, —a combination, in fact, of the two 
varieties figured by Gosse, — we would have a near approach to 
the condition of the Bahama form. But there is still another 
difference. In the European Gem there are only six light-colored 
bands, whereas in the form I have described these are twelve in 
number. This seems a serious discrepancy; but an approach 
towards such a condition is to be found in the European forms. 
In these the warts of the secondary series are usually some- 
what paler than those of the tertiary series, and if the paleness 
should become as marked as in the primary series, and have 
extended so as to include the series on either side, we should 
have the arrangement which is found in the Bahama specimen. 
The presence of a fifth series of tubercles, or, in other words, 
of 96 series of tubercles, seems to be a more important charac- 
ter than that of the coloration. In the European forms appar- 
ently the number of series is invariably 48; but whether this is 
sufficient for the establishment of a new species seems to me 
doubtful. The discrepancies of coloration, too, may be depen- 
dent upon the presence of the extra series of tubercles. 
Even allowing, however, these possibilities, B. zenzatus must 
be considered a decidedly aberrant variety. I have thought it 
advisable, however, to consider it a distinct species, particularly 
on account of the difference in the structure of the tubercles, 
which has been referred to above. The erection of a new 
species from the study of a single specimen is usually a dubious 
matter, and it is quite possible that the examination of a num- 
ber of specimens, and a further study of the histological struc- 
ture of the tubercles of B. gemmacea will necessitate the union 
of the two forms. 
