Ixii 
SYNOPSIS OF GENERA. 
1852. Posidonomya, Pacht. Ueb. Dimerocrinites. 
1852. Posidonomya, Kotorga. Geogn. Kai-te Gouvern. Petersbourg. 
1855. Estheria, Jokes. Quart. Jourii. Geol. Society. 
l%o^.(l)Postdonia, Von Helmbesen. Geogn. Untersuch. Mittl. Gouvern. Russl. 
1859. Estheria, Jones. Quart. Journ. Geol. Society. 
1860. Asimisia, Pander. Monogr. der Saurodipterinen. 
1862. Estheria, Jones. Monogr. Foss. Estherise. 
1882. Estheria, Clarke. Amer. Journ. Science. 
1883. Estheria, Packard. Monogr. North Amer. Phyllop. C)-ustacea. 
Diagnosis. Carapace bivalvular, the outline of each valve being sub-circular, 
obliquely oval or sub-quadrate. Beaks generally anterior, sometimes sub¬ 
central. Dorsal or hinge-line straight, shorter than the greatest length of the 
valves. Surface rarely smooth, usually with concentric lines of growth, the 
interstitial spaces being often ornamented with a fine punctate or reticulate 
sculpture. Test very thin. 
Genus S C H I Z 0 D I S C U S, nov. gen. 
Diagnosis. Carapace bivalvular, the valves readily separable along the hinge. 
Outline circular or ovate, narrowing posteriorly. Surface convex or depressed, 
elevated at the beaks which are prominent, slightly incurved, and situated 
anteriorly. Hinge-line equaling in length the greatest diameter of the cara¬ 
pace ; edges parallel and not gaping at either extremity. Surface ornamented 
by regularly concentric wrinkles. 
ORDER, CIRRIPEDI A. 
Family, Balanid^. 
Genus PROTOBALANUS, nov. gen. 
Diagnosis. Shell ovate about the basis ; composed of twelve plates of which 
the Carina is largest and most elevated. Rostrum small; lateralia five on each 
side ; radial areas between the lateralia broad ; scutum and tergum not known. 
General surface depressed convex. 
