50 Rev. A.M.Norman on new British Species of Ostracoda. 
Mr. Jones, in his ‘Monograph of the Entomostraca of the 
Cretaceous Formation of England,’ has referred the above-de- 
scribed form to his Bairdia subdeltoidea, of which he would con- 
sider it a variety. I cannot acquiesce in this opinion. The 
differences between the typical Bairdia subdelioidea and Cythere 
(Bairdia) inflata are so marked that, even were the two forms 
found living side by side in the same water, I should not hesi- 
tate to consider them distinct, unless connecting intermediate 
forms made it evident that a more than usual latitude must be 
allowed to the variations in this species. With how much greater 
reason, then, must we consider them distinct when the two forms 
are separated from each other not only by the great diversity of 
structure, but also by the geological eons which have elapsed 
between the period of the Chalk formation and the present time. 
Cythere (Bairdia) mytiloides, n. sp. PI. III. figs. 1-8. 
Forma angusta, elongata, mytiloides (et figura et colore); margo 
dorsalis arcuatus, ventralis subrectus ; antice multo altior, hine ad 
extremitatem attenuatam posticam gradatim diminuens. Forma 
desuper spectata compressa, lanceolata, ante medium latior. La- 
titudo altitudine multo minor. Valvarum superficies levis, per- 
paucis pilis modo obsita. Valvarum commissura vix sinuata. 
Color purpureo-badius. Long. circiter 3; unc. : 
Habitat fretum, qui Firth of Clyde vocatur, in Scotia occidentali. 
Carapace narrow and produced, highest in front, and thence 
tapering gradually to a nearly pointed posterior termination } 
the ventral margin is nearly straight, and the dorsal margin 
slopes with a gentle curve to meet it behind. The form, as seen 
from above, is lanceolate and compressed, the widest part situ- 
ated before the middle. The breadth is much less than the 
height. Surface of valves nearly smooth, with merely a few 
closely appressed hairs, which seem, moreover, to be confined to 
the hinder part of the shell. The juncture of the valves forms a 
slightly waved line. Colour purplish brown. Length about 
tp ich. 
In form, in colour, and in general appearance, this species is 
very like a young mussel-shell. 
Found amongst shell-sand dredged in Lamlash Bay, 1854. 
Genus CytHErets (Jones). 
Cythereis fimbriata (Roemer). PI. III. fig. 9. 
Brit. Mus. Cat. Brit. Crustacea, p. 109. 
Cytherina fimbriata, Roemer, Jahrb. (fid. Jones). 
Forma oblonga; margo dorsalis concavus, ventralis subarcuatus ; 
margines posticus et anticus oblique truncati, ita ut ventralis margo 
utrumque versus dorsalem longitudine superat. Valvarum superfi- 
