PALEOZOIC TIME — LOWER SILURIAN. 



499 



610. 



ments of branches of the slender polypary. The diameter of the form Fig. 



604, when living, and having its arms of full length, may have been 15 to 20 



inches. 'Pigs. 607, 608 represent a species of the two-edged forms (Diprio- 



nidse), that is, those having cells along both margins. 



Besides Graptolites, there were massive Ilydrozoan corals, of the Stroma- 



topora type, related, it is supposed, to the modern Millepora. 

 Under EcMnoderms, there were 



Crinoids and Cystoids, and also the 



earliest known of American Star- 

 fishes (Fig. 610). Among the Brachi- 



opods, a common species is the OrtJiis 



{Billing sella) grandceva (Fig. 611). 

 Gastropods, of flat or short spiral 



forms, like Figs. 612-614, of species 



of the genus OpMleta and Madurea, 



were common, and some were of large 



size. The genus Platyceras continued 



on from the Cambrian. There were 



also spiral forms of the genera Pleu- 



rotomaria, Mnrchisonia, Holopea (Fig. 615), and others of the 

 Bellerophon family. The shells of Cephalopods in the Cal- 

 ciferous beds occur of many and varied forms, and some are 

 over a foot in length. Those of the genus OrtJwceras are 

 straight or slightly curved. In 0. primigenium of Vanuxem, 

 first described from the Mohawk Valley, N.Y., the septa, as 

 shown in Fig. 618, are closely crowded. A curved species is 



represented in Fig. 620, Cyrtoceras (?) Vassarinum from Dutchess County, N.Y. 



Stenaster Huxleyl (x 4). Billings. 



en. 



Orthis (Billings- 

 ella) grandaeva. 



612 



612-616. 



612 a 



614 



Gastropods. —Fig. 612, 612a, Ophileta complanata (1), opposite sides; 61S, O.levata (1); 614,0. uniangulata 

 (1); 615, Holopea dilucula. — Ostracoid Crustacean: 616, Leperditia Anna enlarged, side view; 616a, 

 same, upper view ; 616 6, several of the shells, natural size. Figs. 612, 612 a, Whitfield ; 613, 614, 615, Hall ; 

 616, 616 a, b, T. E. Jones. 



There were also coiled species, both the open-coiled of the genus Lituites, 

 and others that were close-coiled, Nautilus-like. Lituites (?) imperator B., 

 Philipsburg, Canada, had a diameter of lOi inches. 



