LOWER SILURIAN. 189 



b. Rhizopods. — The Green sand of some Calciferous beds is good evidence of the ex- 

 istence of Rhizopods (p. 177). Receptaculites Calciferus B., Mingan Ids., is sup- 

 posed by some to be related to the Rhizopods; it looks like a coral pitted closely with 

 small squarish depressions. Dawson suggests that Arch&ocyathus and Stromatopora 

 may be Rhizopods and related to Eozoon. The Stromatopora are massive corals, very 

 finely porous; species of this era occurs at Phillipsburg, Canada. 



Radiates. — a. Polyps. — No Polyp-corals have been found. The genus Stenopora 

 is represented among the Canada beds and at the Mingan Islands ; but it is probably 

 a genus of Acaleph-corals, — that is, the stony secretion of Hydroid Acalephs (see 

 p. 130). 



b. Acalephs. The Stenopora, just alluded to. Also Graptolites, a tribe very nu- 

 merously represented in the Quebec group. 



Echinoderms. — Crinoidal remains are not common. Among them, Billings has dis- 

 tinguished some stems that probably belong to the genus Glyptocrinus (see Fig. 373 

 for a species of this genus). 



Mollusks. — o. Bryozoans. — Some authors place the Stromatopora here. 



b. Brachiopods. — Fig. 289, Orthis (Orthisina?) grandmva B. ; Lingidella acuminata 

 Con , Orthis parva ? Pander, Camarella calcifera B., a species of Leptama, and one of 

 Strophomena. 



c. Lamellibranchs. — One of the earliest of this group is the Conocardium Blumen, 

 bachii B., found on the coast of Newfoundland in limestone (p. 184), a shell related 

 to Cardium, and having a siphonal tube. This division, the sinupallial, was far less 

 common in the Silurian than the integripallial or that in which the tube was wanting; 

 and it is therefore the more remarkable that one uf the earliest of species should have 

 this high characteristic. 



d. Gasteropods. — Many genera of Gasteropods are represented in the Calciferous 

 rocks : and, in all, the aperture of the shell is without a beak. These genera are in part 

 of the Trochus family. 



The following are characteristic species : Fig. 290, Helicotoma ( Euomphalus formerly) 

 unianyulata H. ; 291, Ophileta levataY.; 0. complanataV.; O.compactaS., a tine species 

 from Canada, lh inches across; 292, Holopea dilucula H.; Pleurotomaria Calcifera B., 

 from near Beauharnois, Canada; P. gregaria B., from St. Ann's, Canada, extremely 

 abundant; Maclurea matutina H., from New York and Canada; Murchisonia Anna B. 

 (a long turreted shell, approaching the M. bellicincta, Fig. 346), from St. Ann's on the 

 island of Montreal, and also the Mingan Islands, in the White limestone and the sand- 

 rock below. Species of Straparollus, Murchisonia and Raphistoma occcur in the third 

 bed of the Magnesian limestone of Missouri (Shumard). 



e. Pteropods. — Ecculiomphalus Canadensis B. (a shell three inches long, having the 

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

 species. 



f. Cephalopods. — Figs. 293, 295, Orthoceras primigenium V., a species having the 

 septa or partitions very closely crowded; 294, 0. laqueatum H. Other species are 0. 

 Lamarchi B. ,• 0. Ozarkense Shum., from third bed of Magnesian limestone, Ozark 

 County, Missouri; Lituites Farnsworthi B., a large species partially coiled, and nearly 

 five inches in its longer diameter; L. imperator B., a still larger species, 10J inches 

 across, having the first three whorls coiled in contact; these Lituites are from the 

 upper part of the Calciferous sandrock of Phillipsburg, Canada East. Nautilus Pom- 

 ponius B., about 3 in. across, from Phillipsburg; N.ferox B., Mingan Ids. 



Articulates. — O-ustaceans: Trilobites. — Over 100 American species of Trilo- 

 bites of the Canadian Period have been described; and 14 of these occur in the Calcif- 

 erous. Among these 14, there are 2 species of Amphion and 6 of Bathyurus, both 

 Primordial genera; and 1 of Asaphus (A. canalis), a genus more fully represented in 

 the Trenton period. Species of Agraulos and Conocoryphe occur in the third mag- 

 nesian limestone of Missouri (Shumard). The Ostracoid Leper ditia Anna Jones (Figs. 

 296, 297, 298) occurs at St. Ann's, Island of Montreal. 



