ANDREWS: ANNULUS VENTRALIS. 
465 
like that of C. afjinis. A layer of epidermal cells everywhere covers 
this mass and underlies the exoskeleton. The bulk of the mass is a 
loose areolated connective tissue with its spaces full of blood and it is 
interspersed with large lacunae. Above the epidermal groove of the 
annulus runs the sternal artery and above that the nerve cord, just as 
in C. affinis (text-figures B and C). 
Though so simple, the annulus of C. clarkii is not bilaterally sym¬ 
metrical. While the suture begins and ends on the middle line, it 
sweeps off to one side (pi. 47, fig. 34) and the trumpet (pi. 46, fig. 24; 
pi. 48, fig. 36) is differently disposed on the right and the left of the 
animal since the formative epidermal groove (pi. 48, fig. 40) has much 
of its course upon only one side of the median plane. And, as in the 
previous two species, the open part of the suture, that is the orifice, 
is slightly to one side of the median plane. Of twenty-nine specimens, 
sixteen had the large loop of the suture passing to the animal’s left 
and thirteen had it to the right. In the former (pi. 47, fig. 34) the 
orifice was somewhat on the animal’s right and in the latter somewhat 
on the animal’s left (pi. 46, fig. 24). While the position of the orifice 
is not far from the median plane and its determination often uncer¬ 
tain, there are undoubtedly right- and left-handed specimens in this 
species, and, so far as observed, a slight majority had the large bend 
of the trumpet on the left and the orifice on the right so that they 
might be called right-handed in the same sense as the majority of C. 
affinis. 
Structure in Cambarus bartoni. —Specimens from Baltimore Co., Md., 
studied in April and May were from 60 to 73 mm. long in four cases 
and smaller in the others. Some had no sperm in the annulus and 
others had some sperms in the recess and tip of the tube only (pi. 46, 
fig. 25). The breeding season is much earlier and this retention of 
sperm in the recess is the same phenomenon met with in C. affinis. 
In shape, the annulus (pi. 48, fig. 41) is markedly rhomboidal in 
outline, well elevated and truncated. It has a depressed area posterior 
to the center. Its anterior face (pi. 48, fig. 43) is a long slope reaching 
to the center, while its posterior face (pi. 48, fig. 44) is steep and high. 
A marked but narrow median groove runs up the anterior face and 
then bends to one side on entering the depressed area. This area is 
bounded by a high rounded rim posteriorly and on the sides as well as 
anteriorly, but on the median line anteriorly the rim is interrupted by 
the above groove (pi. 48, fig. 43). 
