Paleozoic Bivalved Entomostraca. 249 
oblique direction backwards and downwards, making the ven- 
tral region full behind. The umbo, or starting-point of the 
concentric ridges, is just within the anterior third of the dorsal 
region, and therefore at some distance from the antero-dorsal 
angle. In these characters this Hstherta approaches such a 
form as the small /. Forbesti figured in the Monogr. Foss. 
Esth. pl. iv. fig. 10; but it does not exactly match any that I 
know of. It is too sharp anteriorly, and too long and broad 
from the front angle to the hinder ventral margin, for &. 
tenella (ibid. pl. i. fig. 26), to which, though larger, it other- 
wise bears some resemblance. 
The ornament of the interspaces between the numerous 
concentric lines of growth consists of very fine dots, or punc- 
tation, like that in H. striata (abid. pl. 1. fig. 24) ; and, indeed, 
that of 1. tenella is not very different (bed. pl. i. fig. 27, and 
pl. v. fig. 7). This interesting paleeozoic Hstheria from Spitz- 
bergen may well bear the name of its discoverer and be known 
as 1. Nathorstt. 
EXPLANATION OF PLATES VI. & IX. 
Puate VI. Fossil Entomostraca from Siberia (Eastern Ural). 
Fig. 1. Estheria minuta (Alberti), var. Karpinskiana, nov. a, left valve, 
SANK was oth. Se A 
magnified 7 diam.; 6, portion, magn. 50 diam. The dorsal line 
should have been horizontal. 
Fig. 2. Estheria striata (Minster), var. tenwipectoralis, nov., magn. 
ae 
7 diam. 
Fig. 3. Entomis gyrata (Richter). a, hollow impression of a valve, 
magn. 20 diam.; 6, portion, magn. 50 diam. 
Fig. 4. Entomis serratostriata (Sandberger). a, convex cast of left valve, 
magn. 20 diam.; 6, portion, magn. 50 diam. 
Fig. 5. The same. Convex cast of a small valve, magn. 20 diam. 
Fig. 6. Primitia? Convex valve or cast, magn. 20 diam. 
Fig. 7. The same (?). Convex valve or cast, magn, 20 diam. 
PuaTE IX. Fossil Entomostraca from Spitzbergen. Figs. 1-8 from 
Klaas Billen Bay. 
Fig. 1. Leperditia tsochilinoides, nov. sp. Left valve, nat.size. This is one 
of the best preserved in shape, but has probably been somewhat 
narrowed in front by oblique pressure. 
Fig. 2. The same. Obliquely squeezed ; right (?) valve, nat. size. 
Fig. 3. The same. Much squeezed obliquely; right valve, nat. size. 
Fig. 4. The same. Small left valve, narrowed by pressure, magn. 
23 diam. 
Fig. 5. The same. Left (?) valve, narrowed and crushed by oblique pres- 
sure, nat. size. 
Fig. 6. The same. Ina block, variously squeezed, nat. size. 
Fig. 7. The same. Ina block, squeezed endwise &c., nat. size, 
Fig. 8. The same. Hollow cast, with remnant of a valve, nat. size. 
Fig. 9. The same. a, right valve, from Liebde Bay, magn. 24 diam. ; 6, 
longitudinal section of a bivalved carapace, magn. 23 diam. ; ¢, 
oblique transverse section near the end of another specimen, 
magn. 23 diam. 
Fig. 10. Estheria Nathorsti, noy. sp., from Mimers dal. a, right valve, 
flattened, magn. 5 diam. ; 6, portion, magn. 50 diam, 
