995 
males; with the females the posterior part is higher. The dorsal 
edge straight; the ventral one convex or somewhat concave. The 
anterior edge equally curved and passing almost unperceptibly into 
the dorsal edge, as together with it a very obtuse angle is formed; 
the posterior edge less curved and forming almost a right angle 
with the dorsal edge. Valves unequal; the right one on the anterior 
part with a half eireular noteh, in which a process of the left valve 
fits. Owing to this peculiar connection of the valves complete carapaces 
have generally been preserved. The sharp hinge line of the left 
valve lies in a furrow on the hinge line of the right valve, the 
latter being higher than the left one along the hinge line. The sharp 
free edges of the right valve lie in a furrow on the free edges of 
the left, so that with the free edges the left valve overlaps the right 
one. The surface of the carapaces is different. On the anterior part 
of each valve two more or less vertical furrows are found that are 
separated by a narrow lobe. Also on the posterior part a furrow may 
occur which can be linked to the anterior furrow below. For the 
rest the surface is generally smooth and without ornamental markings. 
Remains of these Ostracoda have been found in upper silurian, 
devonian and probably also in carboniferous strata of the temperate 
zones of the Northern Hemisphere. 
In the foregoing we have seen that Poloniella devonica can easily 
be derived from the upper silurian Poloniella hieroglyphica by 
assuming that the two small furrows which are found below the 
middle of the three larger ones, are joined together and with the 
anterior and posterior furrow, through the disappearance of the 
intermediate lobes. | 
Poloniella hieroplyphica is sure to have found its origin in a 
species of this genus which resembled to a degree the older but yet 
upper silurian Poloniella Hallii Jones sp. (Fig. 12) (5, p. 15). Here 
the two small furrows are wanting, bui the three larger ones are 
already well developed. The occurrence of valves with one small 
furrow in Poloniella hieroglyphica points to this fact also (Fig. 6). 
The forms resembling Poloniella Halli: can be easily derived from 
the type represented by Poloniella pennsylvanica (Fig. 13) (6 p. 341) 
which occurs in under-devonian deposits and where no more than 
two vertical furrows are present. 
Finally I give my best thanks to Prof. Dr. J. H. Bonnema for 
kindly putting the material of Poloniella hieroglyphica at my disposal, 
and to Miss A. J. Porr, who has been so obliging as to make the 
necessary drawings. 
Mineral.-Geol. Inst. University at Groningen. 
