240 PALEOZOIC TIME. 



Characteristic Species. 



1. Protozoans — Stromatopora. 



2. Radiates. _ (a.) Polyps. — Among Corals, there are species of Zaphrentis, 

 Favosites, Halysites, Syringopora, Chcetetes. (b.) Echinoderms. — Group of Cystideans: 

 Fig. 457, Apiocystis Gebhardi Meek, found in the Lower Pentamerus; Fig. 458, Anoma- 

 locystites comutus H., a remarkable species from the same rock. Of Crinideans, there 

 are species of the genera Mariacrinus, Platycrinus, Edriocrinus, Aspidocrinus etc. 



3. Mollusks. — Brachiopods. — Fig. 459, Hemipronites {Stro2>homena) radiata c( 

 the Catskill shaly limestone; 460, 461, Rhynchonella ventricosa H. of the Upper Penta- 

 merus; 462, 463, Pentamerus galeatus H, of the Lower Pentamerus; 464, 465, P. 

 pseudo-galeatus H., of the Upper Pentamerus; 466, Eatoni-x singularis H., of the Cats- 

 kill Shaly; 467, Meristetta sulcata H., of the Water-lime; 468, Orthis varicn H., of the 

 Catskill Shaly; 469, Spirifer macropleura H., ibid.; 470, Meristella levis H., ibid. 



There are also Lamellibranchs of the genus Avicula, and others related; Gasteropods 

 of the genera Platyceras, Platyostoma, Holopea, etc. Also the Pteropod, Tentaculites 

 irregularis H. (Figs. 471, 472, the latter natural size). 



4. Articulates, — (a.) Trilobites. — Dalmanites pleuroptyx, near Fig. 254; others of 

 the genera Calymene, Ceraurus, Asnphus, Homilonotus, Phacops, Lichas, Acidaspis, 

 Proetus, etc. {b.) Other Entomostracans. — Fig. 474, Eurypterus remipes Dekay, of 

 the Water-lime, natural size, from a small specimen from the cabinet of E. Jewett. 

 Several other species occur in the Water-lime ; also species of the allied genus Ptery- 

 gotus (Fig. 482 is a foreign species), and of the genus Ceratiocaris. Fig. 473, Leper-- 

 ditia alta H., an Ostracoid, abundant in the Water-lime ; besides other Leperditice, and 

 several species of Beyrichia, related Ostracoids. 



The following is a list of characteristic species of the subdivisions: — 



1. Water-lime. — Meristella sulcata, Leperditia alta, Tentaculites irregularis, various 

 species of Eurypterus and Pterygotus. 



2. Lower Pentamerus. — Apiocystis Gebhardi, Rhynchonella semiplicata H., Pentamerus 

 galeatus, species of Lichenalia f 



3. Catskill Shaly Limestone. — Hemipronites radiata, II. punctulifera, Meristella levis, 

 Eatonia singularis, Spirifer macropleura, Sp. perlamellosus H. (formerly rugosus), Platy- 

 ceras ventricosum Con., Dalmanites pleuroptyx H. (formerly D. Hausmanni). 



4. Upper Pentamerus. — Pentamerus pseudo galeatus, Rhynchonella ventricosa, R. no- 

 bilis H., Spirifer concinnus H. 



Atrypa reticularis and Strophomena rhomboidalis are among the few species of the 

 Niagara period which occur in the rocks of the Lower Helderberg. 



III. General Observations. 



Geography. — In the Salina period, as already explained, the lime- 

 stone-making seas of the Niagara period in New York had been suc- 

 ceeded by a great range of muddy flats and shallow basins ; and, in the 

 West, the basin had apparently become much contracted in area, judg- 

 ing from the limited extent of the Salina beds. Neither of these forma- 

 tions reaches to eastern New York. 



In the Lower Helderberg period, which succeeds, there was a return 

 of the conditions for making limestones ; but, in striking contrast with 

 the formations that preceded, the beds have their greatest thickness in 

 eastern New York, and none occur in western. The Lower Helder- 

 berg limestones are mainly Appalachian formations ; for even the 

 New York part is directly in the range of the Appalachians of Penn- 



