304 



PALEOZOIC TIME. 



4. Articulates. — Trilobites, of the genus Phillipsia, and Ostracoids, of the gen- 

 era Cythere, Beyrichia. A bed of limestone, four feet thick, north of Pella, Iowa, is 

 mostly made up of shells of a Beyrichia. The Crustaceans allied to Ceratiocaris, from 

 the top of the " Black Slate," in Kentucky (p. 267), though referred to the Devonian, 

 may possibly belong rather to the Subcarboniferous. 



The Insect, Pnolia vetusta Smith (Fig. 599), is from the whetstone beds of Orange 

 County, Indiana, which have also yielded large numbers of tracks of Insects and Crus- 

 taceans, with some trails of Mollusks. These beds are of the age of the Chester group. 



5. Vertebrates. — Fishes. — The species of American Subcarboniferous Fishes 

 have been described mainly by Newberry, and Newberry & Worthen. They include 

 Hybodont Selachians, of the genera Diplodus, Carcharopsis ; of Cestracionts, of the gen- 

 era Orodus, Helvdus, Cochliodus, Sandalodus, Psammodus, Deltodus, Cladodus, etc. ; and 

 Petalodonts, of the genera Petalodus, Petalorhynchus, Antliodus, Chomatodus, etc., be- 

 sides spines of the genera Leptacanthus, Ctenacanthus, Homacanthus, JDrepanacanthus, 

 Gyracanthus. The species described by Newberry & Worthen, from Illinois specimens, 

 are sixteen of Hybodonts, twenty- six of Petalodonts, and fifty-two of Cestracionts, 

 with nine of fin-spines. Fig. 600, tooth of Cochliodus nobilis N. & W., from Illinois. 

 Fig. 602, Cladodus spinosus N. & W., from the St. Louis limestone, Missouri ; a, section 

 of the same; Fig. 601, Carcharopsis Wortheni Newb., from Huntsville, Ala., Fig. 603, 

 Orodus mammillaris'N.&W., from the Warsaw limestone, Warsaw, Illinois. 



Amphibians. — Fig. 604, tracks of Sauropus primcevus Lea, one-eighth natural 

 size, discovered near Pottsville, Pa., by Isaac Lea, who has published a memoir 

 upon them in large folio, with a full-sized engraving of the slab. 



The Subcarboniferous limestones of Nova Scotia and New Brunswick contain some 

 fossils tbat ally the fauna more with the European than with that of the Interior Conti- 

 nental basin of North America. Among them are the Spirifer glaber Sow. (Fig. 554) 

 and Productus Martini Sow., both of which are European species. 





m. General Observations. 



Geography. — As, in the first half of the Upper Silurian, there was 

 a period — the Niagara — when a sea, profuse in life, and thereby 

 making limestones, covered a large part of the Interior Continental 

 basin ; and again, in the early part of the Devonian age, — the Corn- 

 iferous period, — the same conditions were repeated ; so, in the early 

 Carboniferous, there was a similar clear and open mediterranean sea, 

 and limestones were forming from the relics of its abundant popula- 

 tion. In the period of the Upper Silurian referred to, the living spe- 

 cies were of a miscellaneous character, Brachiopods, Crinoids, and 

 Corals occurring in nearly equal proportions ; but in that of the De- 

 vonian, Corals were greatly predominant, and in that of the Carbon- 

 iferous, Crinoids had as remarkable a preeminence. By an open sea 

 is meant one having free connection in some part with the ocean ; and 

 this connection must have been on the south, toward the Mexican 

 Gulf; for the arenaceous deposits of the wide Appalachian region 

 show that the opening eastward into the Atlantic was for the most 

 part imperfect. The mediterranean sea alluded to was, in fact, only 

 an extension northward of the Mexican Gulf. 



As the Subcarboniferous period opened, the conditions of the Later 



