Silurian life is the continuation and advance of the'same organic system as flourished in the Ordovician, certain groups diminishing, others expanding; and some new groups now make their first appearance sonoceras americanum Foord, x 3/8, Guelph. 17, Trochoceras desplainese McChesney, x 1/2, Guelph. 19, Lichas breviceps Hall, x 1/2, Lockport. 20, Staurocephalus murchi-soni, Barrande, x 1, Lacknort. 21. Deiphon forbesi Barrande, x 1, Niagaran of Arkansas.

Plate VIII.   Silurian Fossils.

Plate VIII. - Silurian Fossils.

Fig. i, Astrceospongia meniscus Roemer, x 1, Lockport. 2, Favosites occidentalis Hall, X 1, Lockport. 3, Halysites catenulatus Linn., x 1, Lockport. 4, Holocystites cylindricus Hall, x 1/2, Guelph. 5, Caryocrinus ornatus Say, x 1, Lockport. 6, Eucalyptocrimis crassus Hall, x 1/2, Lockport. 7, Tentaculites gyracanthus, Eaton,x 5/2, Manlius. 8, Mono-merella noveboracum Clarke and Rued., x 1/2, Guelph. 8a, The same, interior of ventral valve, g, Spirifer radiatus Snwerby, x 1/2, Lockport. 10, .S. crispus Hisinger, x 1, Lockport. 11, Meristina nitida Hall x 1/2, Lockport. 12, Rhynchotreta americana Hall, x1, Lockport. 13, Pentamerus oblongus Sowerby, x 1/2 Clinton. 14, Strophostylus cyelostomus Hall, x 1/2Lockport. 15, Trematonotus alpheus Hall, x 5/8, Guelph. 16, Daw.