OSTRACODA. 669 
Bollia subaquata.] 
sometimes thicker at one end than the other, and the depressions or sulci between 
the ridges relatively narrow. These species pass over into, and the section ought to 
include, some of the so-called quadri-jugate Beyrichiw.* Their relations to Tetradella 
will be considered in the remarks under that genus. 
BoLLIA SUBAHQUATA, 2. Sp. 
PLATE XLVI, FIGS. 26—29. 
Size.—Length, 0.64 mm.; hight, 0.50 Ae thickness 0.22 mm. 
Length, 0.59 mm.; hight, 0.42 mm.; thickness, 0.20 mm. 
Length, 0.40 mm.; hight, 0.32 mm. 
Valves compressed, subovate in outline, straight above; length of hinge some- 
what variable, shortest, apparently, in old examples; dorsal angles more or less 
distinct; edges of valves thick, forming a sharply-defined, thin marginal ridge; inner 
ridge thin, rather long, U-shaped, one of the arms with a slight swelling near or at 
its upper extremity; surface between the ridges flat and without ornament. 
The small valves of this species remind somewhat of Moorea punctata, but as that 
form has no inner or horseshoe ridge they are distinguished very easily. Tetradella 
quadrilirata is a larger form and has the inner ridges joined below with the marginal 
ridge. The nearest allies occur in the Upper Silurian deposits of Europe, but it is 
distinct from them all. . 
Formation and locality—Galena shales (Clitambonites bed), near Cannon Falls, Minnesota. 
Boia UNGULOIDEA, %. Sp. 
. PLATE XLVI, FIGS. 23—25. 
S1zE.—Length 0.6 mm.; hight 0.4 mm.; thickness 0.35 mm. 
Valves subovate, with equal rounded ends, a rather short, straight hinge, and 
illy defined dorsal angles; marginal ridge thick, rounded, a little wider at one end 
than at the other; inner ridge strong, one end swollen, the other small and failing 
to reach the dorsal edge; interspace between the two ridges very narrow. 
* With the exception of several very doubtful species described by Krause, the known species fall into these sections, 
as follows: 
SECTION 1. SECTION 2. SECTION 3. 
. pumila Ulrich, L. Sil. 
. uniflexia Jones and Holl, U. Sil. 
. sicollina J. and H., U. Sil. 
. interrupta Jones, U. Sil. 
bilobata Jones, Dey. 
hindi Jones, Dev. 
. obesa Ulrich, Dev. 
. yranifera Ulrich, L. Carb. 
. unguloidea Ulrich, L. Sil. 
. regularis Emmons sp., L. Sil. 
. persulcata Ulrich, L. Sil. 
. subcequata Ulrich, L. Sil. 
. semilunata Jones, Antic. 
. vinei, Jones and Holl, U. Sil. 
. vinet var. mitis J. and H., U.Sil, . duplex Krause, U. Sil. 
. semicircularis Krause, U. Sil. . 8symmetrica Hall sp., U. Sil. 
. rotundata Krause, U. Sil. Beyrichia clarki Jones, U. Sil. 
Beyrichia halli Jones, U Sil. 
B. ungula Jones, Dev. 
?Beyrichia devonica Jones, Dev. 
Beyrichia subquadrata Jones, Dev. 
Hob bb 
ob tt 
bd td bd ob 
