New and Little Known American Paleozoic Ostracoda. Lr? 
from the first in one respect only: The postero-dorsal extremity 
of the marginal ridge rises into a strong spine-like or otherwise 
shaped process. ‘This process is always flattened either vertically 
or laterally, generally directed a little forward, and beaded on the 
edge. The postero-median ridge, though inclined to be variable, 
is, however, always present. And yet, in all the figures of Beyrichia 
oculifera, or Tetradella oculifera as it should now be called, so far 
published, the narrow sulcus separating it from the base of the 
high process is not represented. Even so experienced an observer 
as Prof. T. Rupert Jones, who lately published figures of the 
epeerecn(@uart. jour, Geol. Soc., Vol. XLVL., Pl. IV., 1890), 
failed to see it. This may be due to the fact that the sulcus is 
usually filled with remains of the shaly matrix; or it may have 
been obscured by the shadow of the prominence just above it. 

Fig. 1. Ventral edge of a complete carapace of Tetradella oculifera, 
(Eta Sse BS. 
The classificatory value of the elevated process that characterizes 
the second section of this genus is questionable. It is scarcely a 
feature of generic importance, yet, as its peculiarities in each 
of anumber of species or varieties are remarkably constant, we 
are not justified in viewing it as a ‘‘mere ornament.’ At one 
time I thought of distinguishing the species generically as Cera- 
tela, but further study has convinced me that such a division is 
unwarranted at the present time. 
Taking the genus as a whole, its relations are perhaps nearest 
Ctenobolbina, the anterior half of the valves being sometimes much 
alike in the two. The posterior halves, however, are quite differ- 
ent, the bulbous character of that part of the carapace in Cfeno- 
bolbina having no representation in Ze¢vadella. The ridges also are 
always more clearly defined in species of the latter. 
In true species of Leyrichia there is no sub-marginal ridge, the 
