PALEOZOIC TIME — UPPER SILURIAN. 



549 



Lamellibranchs are not numerous, — a common fact with limestones. 

 One of them from the Coralline limestone, and also from Guelph in Ontario, 

 is shown in Fig. 781 ; another more common form, an Avicula, in Fig. 782. 

 Figs. 783, 784 are of two Gastropods, the latter also a Clinton group species. 

 A Pleurotomaria (P. solarioides) , from the Guelph limestoue, has a diameter 

 of four inches. There were also Conularice of unusual size. Cephalopods 

 include species of Orthoceras, Actinoceras, Discosorus, Huronia, Gomphoceras, 

 Troclioceras. 



The following iigures, 785-789, are the forms of some of the Niagara 

 Trilobites, all reduced one half or more. The Lichas Boltoni (Fig. 786) has 

 sometimes a length of seven inches, and the Homalonotus (Fig. 787), remark- 

 able for its small eyes, even a greater length. The Calymene Niagarensis is 

 very similar to the G. calUcephala of the Trenton period (Fig. 690) . 



785-789. 



Teilobites. — Fig. 785, Dalmanites limulurus (x i) ; 786, Lichas Boltoni (x J) ; 787, Homalonotus delpWno- 

 cephalus (x \) ; 788, lUsenus loxus (x J). Ckustacean. — 789, Beyrichia symmetrica; 7S9 a, same, natural 

 size. HaU. 



Ceratiocarids, among Crustaceans, occur of large size. The telson, or 

 tail-spine, of one from western New York, Ceratiocaris Deweyi, is over six 

 inches long, indicating a length for the Ceratiocaris of nearly two feet, or as 

 great as that of C. Angelini (Fig. 729). - 



Characteristic Species. 



1. Medina Epoch. 



Fig. 744, Arthrophycus Harlani H. (1853) = Harlania Halli Gcepp. (1852) = Fxicoides 

 Harlani Con. (1838). Fig. 739, Lingula cuneata Con. ; Atrypa ( Whitjieldella) oblata H. ; 

 740, Modiolopsis orthonota Con. ; 741, M. primigenia Con. ; 742, Pleurotomaria litorea H. ; 

 P. pervetusta Con.; 743, Bucania trilohata Con., different views ; Oncoceras gibhosum H. ; 

 Orthoceras multiseptum H. 



2. Clinton Epoch. 



Plants. — Buthotrephis gracilis H., B. ramosa H. A Lycopod (or Fern) has teen 

 reported from Ohio by E. W. Claypole (1878). It is of doubtful nature. 



