PALEOZOIC TIME — DEVONIAN. 



597 



from Manitoba specimens described by Whiteaves ; the latter figure shows 

 the natural outer surface, consisting of hexagonal plates, and the former, 

 the interior ; Fig. 902 c, is from a portion of the exterior enlarged, and 902 d 



902 



902-902 c. 



902 c. 



Spongiozoan. — Fig. 902, a, Spliserospoiigia tesselata ; b, enlarged view of exterior hexagonal plates ; c, enlarged 



view of spicules. Whiteaves, '92. 



908. 



represents the cruciform spicules. The genus is put in the same group with 

 Receptacidites, by Eaiiff, who doubts, as in the case of that genus, the sup- 

 posed relation to Sponges, and states that the spicules were originally calca- 

 reous. The rock is dolomyte. 



2. Polyp-corals. — Corals are found chiefly in con- 

 nection with the few beds of limestone ; and near 

 Canandaigua, !N".Y., and to the westward, the 

 Hamilton contains large numbers in coral-reef 

 style. Fig. 903 represents a common species of 

 Heliophyllum ; and among the other genera there 

 are Gyatliophyllum, Cystiphyllum, ZapJirentis, Favo- 

 sites, and Michelinia. 



3. Crinoids. — Crinoids occur sparingly, in New ^^ 



York, but more abundantly at the Falls of the HeUophyUum Ham. Edw.and 



. . "^ Hairne. 



Ohio. They include species of Platycrinus, Actin- 



ocrinus, Cyaihocrinus, RJiodocrinus ; also Nucleocrinus, Pentremites, etc. 



4. Molluscoids. — Brachiopods continue to be common fossils. Figs. 



