OSTRACODA. 671 
Drepanella bilateralis.] 
group. With these we may include, without materially altering our conception of 
the genus, the new D. bilateralis, although in this species the characteristic sickle- 
shaped marginal ridge is wanting posteriorly. But the other Minnesota species, D. 
bigeneris, is certainly aremarkable form. In size and general appearance it agrees 
very well with D. crassinoda and D. ampla having the sickle-shaped ridge well 
developed, and two large centro-dorsal nodes, separated by a depression, as in the 
latter species. But the peculiar feature is that these nodes are prolonged below and 
united by a slender connection, giving us precisely the horseshoe ridge of a Bollia. 
The question arising at once is, why should the species not be viewed as a Bollia, 
rather than a Drepanella. 
I have decided for Drepanella on what I believe to be good genealogical grounds. 
In the first place, aside from the ventral connection of the nodes, all the characters 
of the species are those of Drepanella. The marginal ridge, it is true, runs farther 
up on the anterior end than on any of the other species, yet its extremity is thin and 
the mere fact that it is a trifle longer than usual cannot be of much consequence. 
But the most important evidence on the question is furnished by D. ampla var. elon- 
gate, of which a copy of the original figure is given above. In this variety, namely, 
there is a well defined depression between the nodes precisely as in D. bigeneris, and 
all that is required to produce the loop of the latter, is a slight raising of the nodes, 
together with the lower border of the depression. This is not, I believe, supposing 
too much, for a ventral coalescence cf the anterior and posterior lobes or nodes is 
not by any means restricted to Bollia. Indeed it occurred under one form or another, 
among many types of Beyrichiide. That this is true, a glance at plate x~1v may 
suffice to prove. One form is shown in fig. 4, another, and widely different, in fig. 6, 
while 8, 10, 12, 15, 17, 20, 28, 26, and 27 illustrate other types of the same condition. 
DREPANELLA BILATERALIS, 7. Sp. 
PLATE XLVI, FIGS. 35—38. 
Size.—Greatest length 2.7 mm.; length of hinge 2.15 mm.; greatest hight1.64 mm.; greatest thick- 
ness, about 1.38mm.; thickness, not including nodes and ridge, about 0.6 mm. 
Valves suboval or oblong-subquadrate, compressed; dorsal margin -straight; 
distinctly angular at the extremities; anterior end a trifle narrower, and the outline 
less convex than the posterior; ventral margin nearly straight centrally. Running 
parallel with and close to the ventral margin a strong ridge, somewhat thickened at 
each end, but not continuing up the posterior end as in the other species. Above 
this two irregularly triangular and very prominent large nodes extend to the dorsal 
_ edge, beyond which their pointed extremities occasionally project. The lastis true 
also of a small central tubercle. 
