NIAGARA PERIOD — NIAGARA EPOCH. 



241 



(c.) Conchxfera. — Fig. 405, Avicula emaeerata. > s v 



(d.) Gasteropoda. — Fig. 406, Platyostoma Niagarensis; 407, Platyceraa angu- ^\\ 



Figs. 392-404. 



02 



Brachiopods. — Fig. 392, Strophomena rugosa ; 393, Leptaena transversalis ; 394, 395, 

 Atrypa nodostriata; 396, Merista nitida; 397, Pentamerus interplicatus ; 398, a, Rhyn- 

 chonella cuneata; 399, a, 6, Leptocoelia disparilis; 400, a, Orthis biloba ; 401, 402, Spirifer 

 Niagarensis ; 403, 404, Sp. sulcatus. 



latum, a true univalve, but loosely and imperfectly coiled, as shown in the 

 profile view, fig. 407 a. 



Fiss. 405-407. 



Conchifer and Gasteropods. — Fig. 405, Avicula emacerata ; 406, Platyostoma Niagarensis ; 

 407, a, Platyceras angulatum. 



(e.) Cephalopoda. — Species of Orthoceras, Cyrtoceras, Gomphoceras, and of 

 Gonularia. The last probably belongs to the division of Cephalopods having 

 internal shells. 



3. Articulates — (a.) Trilobites. — Fig. 408, Dalmania limulurus (a genus 

 differing from Calymene in having the glabella, or middle region of the buck- 

 ler, largest anteriorly, besides having large reniform eyes and other pecu- 

 liarities) ; 409, Lichas Boltoni, a large and characteristic species, much reduced ; 

 410, Homalonotua delphinocephalus (the genus having very small eyes, the glabella 

 faintly outlined and undivided, — the middle lobe of the body much broader 

 than the lateral) ; 411, Illsenus Barriensia ; Calymene Blumenbachii var. Niaga- 



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