94 
Gustaf T. Troedsson 
3 dorsal ones and 3 ventral ones. In general they are not placed exactly on the 
margins but drawn a little inwards; this is above all the case with the ventral 
ones. The characteristic . distribution of the separate tubercles is shown on the 
figures. The marginal border has not been observed. For the measures see p. 53. 
This species belongs to the group of Ct. subcrassa of Ulrich & Bassler. 
Otenobolbina rara n. sp. 
PL II, f. 18. 
Anterior margin almost straight in its upper part, making an obtuse angle 
with the straight hinge-line. Posterior end rounded and the ventral one gently 
curved. The valve is highest just before the middle. Besides the main sulcus 
which according to direction and form agrees with that of Ctenobolbina sexpapillosa 
although apparently shorter, there is a posterior rather faint impression, almost 
parallel with the former. The low elevation between them, thus having an 
oblique direction forward and downward, is situated in the centre and is the 
most convex part of the valve. Before the main sulcus there is a great tubercle, 
being impressed on the figured specimen and thus having been surrounded by a 
furrow. Behind the shallow impression and near the postventral corner there is 
the basis of a broken, probably conical, outwards directed tubercle. Also on this 
species no marginal border is observed. The only specimen, a right valve, measures : 
Length 1,25, height 0,71 mm. 
Bollia harparum n. sp. 
PL II, f. 19—20. 
Anterior end higher, more convex and with a more' curved margin than the 
posterior one. It is provided with a marginal raised line which while decreasing 
continues ventrally and then bends upwards crossing the shell as a faint transverse 
rib at a distance of a fourth to a third of the length of the shell from the posterior 
margin. Dorsal margin straight, the ventral one more or less uniformly curved. 
Within the raised line and almost parallel with it there is a very strong U-shaped 
elevation, composed of two almost straight lobes, crossing almost the entire valve 
from the dorsal margin and coalescing ventrally. The anterior lobe is the greater 
and more swollen and thus more or less separate, the ventral connection, however, 
never discontinued though still fainter than the lobes. — For the measures 
see p. 55. 
