THRACIA.
37
truncated at the posterior end, with a well-defined angle on
that side ; posterior dorsal margin somewhat recurved, instead
of sloping ; anterior dorsal margin longer : heahs less prominent, with a slighter and less distinct excavation below them
ligament rather large, but short, yellowish-white or pale brown,
keeping the valves asunder on the posterior side, and when
removed leaving a lanceolate gap : cartilage yellowish-brown
;
pits obliquely elongated sideways, and not projecting so far
inwards as in T. pratemm ; connecting ridge at the bottom
thicker and less distinct : ossicle semiannular, placed as in that
species : other particulars the same, except that in the present
species the beaks only (and not the hinge) are fissured, and
the rib-like mark of repair in the interior is therefore wanting,
L. 0-6. B. 1-1.
Var. 1. gracilis.
Shell more slender, and approaching a
cyhndrical shape, thinner, more uniformly convex
;
posterior
end shorter in proportion.
Yar. 2. viUosiuscula.
Thicker, and less elongated transversely ; posterior angle more rounded, but truncated. Anatina viUosiuscula, Macgilhvray in Edinb. New Phil. Journ.
April 1827, p. 370, pi. i. f. 10, 11. T. viUosiuscula, F. & H. i.
p. 224, pi. xvii. f. 4, 7.
Monstr. Furrowed on the posterior slope, or having misshapen valves.
Habitat : Sandy bays in the laminarian zone ; rather
common. Var. 1. Bantry Bay, and twenty miles north
of Unst in 86 f. Var. 2. As widely diffused as the
typical form, but usually in deeper water, or where the
supply of calcareous material is more plentiful. Fossil
at Belfast (Grainger) ; Kyles of Bute, and Lochgilphead
(Geikie) ; Coralline Crag (S. Wood). Both the typical
kind and the variety viUosiuscula range from Iceland to
the iEgean and Canaries, at depths of from 2 to 35 f.
an intermediate form has been taken by Steenstrup in
Iceland, by Malm on the Swedish coast, and by
M^Andrew in Vigo Bay. Mr. Malm^s son found the
variety subfossil at Uddevalla, and Sars in the newer
part of the glacial formation near Christiania.
37
truncated at the posterior end, with a well-defined angle on
that side ; posterior dorsal margin somewhat recurved, instead
of sloping ; anterior dorsal margin longer : heahs less prominent, with a slighter and less distinct excavation below them
ligament rather large, but short, yellowish-white or pale brown,
keeping the valves asunder on the posterior side, and when
removed leaving a lanceolate gap : cartilage yellowish-brown
;
pits obliquely elongated sideways, and not projecting so far
inwards as in T. pratemm ; connecting ridge at the bottom
thicker and less distinct : ossicle semiannular, placed as in that
species : other particulars the same, except that in the present
species the beaks only (and not the hinge) are fissured, and
the rib-like mark of repair in the interior is therefore wanting,
L. 0-6. B. 1-1.
Var. 1. gracilis.
Shell more slender, and approaching a
cyhndrical shape, thinner, more uniformly convex
;
posterior
end shorter in proportion.
Yar. 2. viUosiuscula.
Thicker, and less elongated transversely ; posterior angle more rounded, but truncated. Anatina viUosiuscula, Macgilhvray in Edinb. New Phil. Journ.
April 1827, p. 370, pi. i. f. 10, 11. T. viUosiuscula, F. & H. i.
p. 224, pi. xvii. f. 4, 7.
Monstr. Furrowed on the posterior slope, or having misshapen valves.
Habitat : Sandy bays in the laminarian zone ; rather
common. Var. 1. Bantry Bay, and twenty miles north
of Unst in 86 f. Var. 2. As widely diffused as the
typical form, but usually in deeper water, or where the
supply of calcareous material is more plentiful. Fossil
at Belfast (Grainger) ; Kyles of Bute, and Lochgilphead
(Geikie) ; Coralline Crag (S. Wood). Both the typical
kind and the variety viUosiuscula range from Iceland to
the iEgean and Canaries, at depths of from 2 to 35 f.
an intermediate form has been taken by Steenstrup in
Iceland, by Malm on the Swedish coast, and by
M^Andrew in Vigo Bay. Mr. Malm^s son found the
variety subfossil at Uddevalla, and Sars in the newer
part of the glacial formation near Christiania.