206 



PALEOZOIC TIME. 



from the Cincinnati group. Among Gasteropods, occur Cyrtolites ornatus Con., near 

 Fig. 350; C. imbricatus M. & W., Illinois; Cyclonema bilix Con., Pleurotomaria Amer- 

 icana B. 



Among Pteropods, there are species of Tentaculites, T. tenuistriatus M. & W., and 

 T. Oswegoensis M. & W., from Illinois, in the Cincinnati group. 



3. Articulates. — Among Trilobites, Asapkus platycephalus (Fig. 360), Calymene 

 Blumenbachii Brngt. and Trinucleus concentricus (Fig. 363) continue on from the Tren- 

 ton period; but A. platycephalus is rivalled both as to abundance and size by A. megistos, 

 already referred to, found in Ohio and other States west. A. Canadensis Chapm. is a species 

 from the Utica shale. Triarihrus Bechii is common in the Utica shale, and occasionally 

 seen in the Trenton beds. The head-shield generally occurs without the body : Fig. 380 



Fig. 380. 



Fig. 381. 



Triarthrus Beckii. 



represents its usual form, and Fig. 381 the same entire. The body is much like that of 

 a Calymene (Fig. 361): it has a row of minute spines along the middle of the back. 



The Anticosti limestone is supposed to range in time from the Trenton period through 

 the Niagara, and probably through the Lower Helderberg. Some of the characteristic 

 fossils of its upper four divisions (p. 196) are the following. 



I. Leptcena sericea, Strophomena rhomboidalis, S. pecten Sharpe, Orthis lynx, O. 

 Salteri B., Pentamerus reversus B., BelleropJion bilobatus, B. acutus Sharpe, Pleuroto- 

 maria Americana ;'B., Ambonychia radiata ; and, with these, Halysites catenulata, Fa- 

 vosites Gothlandica Linn, Petraia gracilis B., a Heliolites; also Strophomena subtenta 

 Con., a species occurring in the Cincinnati limestone, and S. recta Con., a Wisconsin 

 (Mineral Point) species. 



II. Favosites Gothlandica, Halysites catenulata, Stromatopora concentrica, a species of 

 Aulopora, species of Cyathophyllum, Orthis Salteri, Strophomena Leda, S. pecten, 

 Pentamerus Barrandei B., Atrypa congesta Con., A. reticularis Linn., Calymene Blu- 

 menbachii, etc. 



III. The same species as in II. of Favosites, Halysites, Stromatopora, Strophomena, 

 Atrypa, Orthis, Calymene, with Orthis elegantula Dalm., Strichlandinia lens Sow., Pen- 

 tamerus oblongus Sow. (a species characteristic of the Clinton group in the Niagara 

 period), Phacops orestes B., Favosites favosa H. Niagara species), Zaphrentis Stohesi B., 

 Alveolites Labechii M'Edw., etc. 



IV. The same species as in III. of Favosites, Halysites, Stromatopora, Zaphrentis, 

 Alveolites, Strophomena, Atrypa, Orthis, Calymene, Phacops, with species of Cyatho- 

 phyllum, Ptychophyllum, etc. 



2. European. 



In Great Britain, the beds of the whole Lower Silurian from the 

 bottom of the Primordial make a single conformable series. Those 

 which appear to be equivalents of the beds of the Trenton period 

 are the Llandeilo flags, 5,000 feet thick ; the Bala beds, or Caradoc 

 rocks, 6,000 feet, and the Lower Llandovery, 1,000 feet. The Llan- 

 deilo flags of South Wales include thin laminated sandstones or flags, 

 and dark earthy slates often gritty, with some beds of limestone. 

 These pass up, without any definite line of demarcation, into the Bala 



