192 



PALEOZOIC TIME LOWER SILURIAN. 



related to Cardium, and belonging to the division of Conchifers having a si- 

 phonal tube. This division, the sinupallial, was far less common in the Silurian 



Figs. 253-260. 



Fig. 253, Orthis (Orthisina?) grandasva; 254, Helicotoma uniangulata; 255, Ophileta levata; 

 256, Holopea dilucula ; 257, 259, Orthoceras primigenium ; 258, 0. laqueatum ; 260, 260 a, 

 Leperditia Anna; 260 b, same, natural size. 



than the integripallial, or that in which the tube was wanting; and it is there- 

 fore the more remarkable that the species first made known should have this 

 high characteristic. Mr. Billings remarks that there are indications on the 

 shell of the existence of the siphon (see p. 157). For illustrations of the genus, 

 see figs. 331 and 457. 



d. Gasteropoda. — Many genera of Gasteropods are represented in the Calcife- 

 rous rocks; and in all the aperture of the shell is without a beak (see p. 156). 

 These genera are in part of the Trochus family. 



The following are characteristic species: — Fig. 254, Helicotoma (Euomphalus 

 formerly) uniangulata H. ; 255, Ophileta levata V. ; O. cowjjlanataY.; O. com- 

 pacta, a fine species from Canada, one and a half inches across; 256, Holopea 

 dilucula; Pleurotomaria Calcifera B., from near Beauharnois, Canada; P. gre- 

 garia B., from St. Ann's, Canada, extremely abundant; Ifacliwea matutina H., 

 from New York and Canada; Murchisonia Anna B. (a long turreted shell, ap- 

 proaching the M. bellieincta, fig. 306), from St. Ann's, on the island of Montreal, 

 and also the Mingan Islands, in the White limestone and the sandrock below ; 

 Ecculiomjjhalus Canadensis B. (a shell three inches long, having the form of a 

 curved horn without transverse partitions within); E. intortus B., a smaller species. 



e. Gephalopods. — This highest tribe of Mollusks is well represented, though 

 less abundantly so than in the next period. The chambered shells of these 

 species in this period are either straight or nearly so, like a long, tapering horn, 

 as in Orthoceras (whence the name, from the Greek opduq, straight, and Kepa;, 

 horn) ; or arched or partially coiled, as in Lituites ; or completely coiled, as in 

 Nautilus. Figs. 257, 259, Orthoceras primigenium V., a species having the septa 

 or partitions very closely crowded ; 258, O. laqueatum H. Other species are O. 

 Lamarcki ; Lituites Farnszvorthi B., a large species partially coiled and nearly five 

 inches in its longer diameter ; L. impcrator B., a still larger species, 10£ inches 

 across, having the first three whorls coiled in contact. These Lituites are from 

 the upper part of the Calciferous sandrock of Phillipsburgh, Canada East. They 

 appear to be among the largest of the Cephalopods, and, along with the Nau- 

 tilus, the highest species of Mollusk in the Potsdam period. 





