Marwick.—Genus Glycymeris in Tertiary of New Zealand. 63 
Arr. 2.—The Genus Glycymeris in the Tertiary of New Zealand. 
By J. Marwick, M.A., New Zealand Geological Survey. 
[Read, by permission of the Director of the N.Z. Geological Survey, before the Wel- 
lingion Philosophical Society, 12th October, 1921 ; received by Editor, 2nd December, 
1921; issued separately, Ist February, 1923.] 
Plates 1-7. 
GLYCYMERIS Da Costa, 1778 (= PEcTUNCULUS Lamarck, 1799). 
Tue genus Glycymeris, appearing first in the Cretaceous, is widely spread 
throughout the Tertiary strata of the world, and exists in the Recent seas 
of the West Indies, Britain, India, New Zealand, Australia, and western 
America. It is a shallow-water shell, ranging, according to Woodward, 
from 8 to 60 fathoms, and rarely to 120 fathoms. Consequently the fossi 
occurrence is generally in fine conglomerates, sandstones, or shell-beds. 
Suter seems to have had an erroneous idea as to which is the anterior 
of the shell. Thus in his description of both G. laticostata and G. modesta 
(1913, pp. 851 and 852) he says the beaks curve “ forward." This is not 
the case. The curvature, though generally slight, is towards the rear. 16 
will not be out of place to quote Fischer (1887, p. 978): “ The impression 
of the anterior adductor is subtrigonal, that of the posterior adductor 
is subtrapezoidal, and limited in front by a projection or ridge which is 
directed towards the umbones and more elevated than the ridge limiting 
the rear of the anterior adductor; the pallial line at its junction with the 
impression of the posterior adductor forms a small sinus; the beaks are 
slightly inclined to the rear." 
her noteworthy features are— 
(1) Worm-borings and malformation are very common on the 
osterior. 
(2.) The ribs are narrower on the posterior. 
raised than those of G. concava, a feature seen only in well-preserved 
i ea 
differing only in their strongly-raised ribs and wide interstices. In this 
respect they approach the laticostata group, and may represent the ancestor 
