12 G 
Description of the species : — 
Class BRACHIOPODA. 
Order CLISTENTERATA. 
Family Spirtferhle. 
Genus Atrypa, Dal man, 1828. 
(Tv. Yet. Acad. Handl., 1827, p. 102.) 
Atrypa reticularis, Linn. 
A. reticularis (Linn.l, Davidson, Mon. Brit. Sil. Brachiopoda, 1867 
Pt. ii., p. 129 (for synonomy), t. 14, f. 1 - 22. 
Obs. — This protean species is numerously represented in the 
Lilydale Limestone, Prof. Tate informs me. We have one 
example. 
Class PELECYPODA. 
Order MYTTLACEA. 
Family Aviculiml 
Genus Ambonychia, Hall, 1847. 
(Pal. N. York, I., p. 163,) 
AmBONYCTTIA ^ POSTSTRIATA, sp. UOV. 
(PI. xviii., tigs. 1 and 2.) 
Sp. Char. — Shell deltoid, or triangularly-mytiliform, alate 
posteriorly, truncate anteriorly. Valves convex in the umbonal 
region ; hinge line straight ; ventral margin convex, rounding fore 
and aft insensibly into the anterior and posterior margins; anterior 
alation wanting, the margin truncated, and somewhat incurved, 
straight walled, and with a large, deeply excavated byssal notch, 
cordate when the valves are in apposition ; posterior end alate, 
more or less flattened, but no concavity along the posterior slope; 
umbones sharp, prominent, and elevated above the hinge line, 
slightly incurved ; body of the shell gently convex from the 
umbones downwards to the ventral margin. Sculpture consisting 
of coarse concentric laminae of growth, uncrossed by any radiating 
or decussating striae, except on the posterior slope, which is finely 
radiate, the intersection with the concentric laminae giving rise to 
a fine fimbriation. 
Obs. — The genus Ambonychia possesses two allies, Anomalodonta, 
Miller, and Opisthoptera, Meek, greatly resembling it in external 
appearance, but differing in the internal structure of the hinge, 
and to either of which the present species might equally well be 
referred, but as we are quite ignorant of the characters of the 
dorsal margin, 1 have thought it better to provisionally place the 
shell in the genus in chief. It differs, however, from all three, in 
