
eT 
B. pala, B. angularis, and probably B. urceolaris, has a variety—in 
fact, several varieties—with two posterior spines which are usually 
symmetrically placed but not always symmetrically developed. The 
form without posterior spines (var. clumorbicularts Skorikow) inter- 
grades with these, and a series might be formed with complete 
intergradations linking this in turn with var. rhenanus Lauterborn, 
in which the spines are but slightly and often unequally developed. 
From this we pass, by a slight elongation of the posterior spines, to 
var. brevispinus Ehrbg., thence to the type in which the spines as 
figured by Rousselet (’97) are directed posteriorly with but shght 
curvature. From this we may pass toward variants in which the 
symmetry is preserved, but the spines are much elongated and 
curved outwardly. The anterior spines in such individuals are also 
more elongated and exhibit a similar outward curvature (var. 
melhemi Barrois and v. Daday). Extreme types of this curvature 
sometimes occur (B. falcatus Zach.). In another direction we find 
the bilateral symmetry of the processes, both anterior and posterior, 
to some extent lost as a result of differences in the curvature of the 
spines (var. tuberculus Turner). There are also differences in the 
surface markings of the lorica which have been utilized as specific 
distinctions. Kertész (’94) describes as B. granulatus a species 
with a minutely pustulate surface, and Turner’s B. tuberculus takes 
its name from this same feature. It seems questionable, however, 
if these surface markings are even of varietal value. Individuals 
without spines, in which the transverse diameter is relatively large 
(var. obesus Barrois and v. Daday), are also found. 
In assorting the individuals belonging to this variable group I 
have arranged them under the following heads: bakert O. F. Mull., 
bidentata Anderson (non bidentatus Kertész), brevispinus Ehrbg., 
cluniorbicularis Skor., melhemi Barrois and v. Daday, obesus Barrois 
and v. Daday, rhenanus Lauterborn, and tuberculus Turner. The 
number might have been increased. The individuals referred to 
var. melhemi include many if not all of the long-spined specimens 
such as Rousselet (97) has referred to the type, the latter designa- 
tion having been given to individuals intermediate between this and 
brevispinus. The variety tuberculus includes the asymmetrical 
individuals, regardless of the surface markings. I will now briefly 
compare the seasonal distribution of these varieties and note 
any peculiarities which mark them individually: 

