Paleozoic Bivalved Entomostraca. 335 
3. Elevations and depressions of surface. 
In Leperditie— 
i, Ocular tubercle and escutcheon. 
ii. Muscle-spot (and internal vascular markings). 
il. Nuchal furrow. 
4, Surface-ornament. 
Reticulation, &e. 
The subjects of the present paper have long been under 
observation, some for many years, and have been brought 
together, by the kind help of friends, from Siluria, Scandi- 
navia, Livonia, Russia, and North America. The drawings 
have been made at different times and on various scales, some 
under a grant from the Royal Society, by the aid of which 
also the careful plates before us have been lithographed. 
I believe that figs. 1, 10, 11, and 4 of Pl. XIX. belong to 
the typical (oblong) L. balthica, and that figs. 2, 3, 13, 14, 
and 17 represent a small and short variety of the same. 
Figs. 5, 6, and 16 are varieties of the more ovate L. Hisin- 
gert, Schmidt. Such dwarfs and varieties of large well- 
marked forms remind us of the great variations to which the 
Carboniferous L. Okent was subjected in the varying seas 
and lagoons of that period. Fig. 9 is a new species from 
N.W. Canada. Fig. 12 is Lsochilina punctata (Hichw.) ; fig. 15, 
L. phaseolus (His.), var. In Pl. XX. figs. 1-3 are simple Pri- 
mitice from Newfoundland; fig. 5 answers to the typical L. 
canadensis; and Pl. XIX. fig. 7, and Pl. XX. figs. 4,7, and 
8, are probably L. fabulites (Conrad). Pl. XIX. fig. 9 is L. 
amygdalina of Canada; and Pl. XX. fig. 6 is a fresh and 
correct drawing of L. Hicks, one of the oldest species of the 
genus. 
1. Leperditia balthica (Hisinger). (Pl. XIX. figs. 1, 4a, 46, 
10, 11: all small specimens.) 
1837. Cytherina balthica, His. Leth. Suec. p. 10, pl. i. fig. 2. 
1854. Cythere baltica, Romer in Bronn’s Letheea Geogn. ii. p, 528 
(parte), pl. ix*. figs. 8, 9. 
1856. Leperditia balthica, Jones, Ann, & Mag. Nat. Hist. ser. 2, vol. xvii. 
p- 85 (parte), pl. vi. figs. 1, 2, 4, 5. 
1869. Leperditia baltica, var. a, Kolmodin, Sveriges Siluriska Ostra- 
coder, p. 14. figs. 1-8. 
1873. Leperditia baltica, Schmidt, Mém. Acad. Imp. Sci. St. Pétersb. 
sér, 7, vol. xxi. no. 2, p. 15. 
Pl. XIX. fig. 10. This is the outline of a small, suboblong, 
left * valve, somewhat broken at the hinder margin, ~% inch 
* The narrower and overlapped valve of the carapace. 
