271 
P. Mering’e, spec. nov.* 
Miocene.—Gippsland Lakes (V.). 
Shell suborbicular in marginal outline, equilateral, inequivalve, 
radially ribbed, ribs in five groups, ears large. 
Riyht valve of about 50 mm. diameter, moderately inflated, 
ventral margin undulating corresponding with the areas occupied 
by the five groups of primary radial ribs and their intervening 
concave furrows. Primary ribs stout, flatly convex, with pre- 
cipitous sides, about 18, variously grouped in twos, threes, and 
fives, forming elevated radial folds; the intervening concave 
areas with one or two slender ribs; the whole surface covered 
with close-set, slender, undulating, concentric lire, more or less 
lamellose on the primary ribs (ten in a length of one mm. at the 
front on the medial line). Anterior ear large, falcate, with three 
or four radial riblets, crossed by concentric lire forming slight 
squame on the riblets and terminating in a serrated crest on the 
dorsal margin. Posterior ear of less size, right-angled triangular, 
ornamented with fine concentric lire. 
Left valve flat, the ornament similar to, but alternating with, 
that of the inflated valve; the anterior ear has, however, stouter 
riblets, and the transverse lire rise into erect lamelliform scales. 
An adult left valve of 95 mm. diameter has five broad elevated 
rays, the ribs of which are finally evanescent, whilst the riblets 
in the interstitial furrows are not so pronounced as in the 
medium-sized valves. 
Dimensions of the figured shell.—Antero-posterior diameter, 
40 ; ventro-dorsal diameter, 35; thickness through both valves, 
10 mm. 
The name of the species perpetuates that of an aboriginal 
locality whence the fossils have chiefly been obtained. 
This species is separated from the bifrons-group by the absence 
of shagreen sculpture ; the clustering of the ribs into sets allies 
it to polymorphoides among our fossil forms, and to undulatus 
and related species among living species of the Janira-group. It 
differs from polymorphoides, its nearest ally, by the regular con- 
vexity of the inflated valve, and by the distinct equilaterality of 
the shell. 
SPECIES EXCLUDED. 
P. spondyloides, Tate, 1886—SpPonDYLUS ARENICOLA. 
P. deformis, Tate, 1887, is a worn H1nnites CorRIoEnsIs. 
SECTION PsEupAMussium, HZ. and A. Adams, 1855. 
Surface smooth, no internal ribs. 
* The illustrations of this and other species diagnosed in the tollowing 
pages are deferred to the issue of the concluding part of the ‘‘ Revision of 
he Lamellibranchiata.” 
