174 



PALEOZOIC TIME. 



247-250. 



a genus eminently characteristic of the Primordial, containing species 

 related to the modern Lingula ; of Discina (Fig. 

 249), disk-shaped shells ; and others of Orthis 

 (Fig. 250) and Obolella. 



Among Articulates, the Worms are fleshy spe- 

 cies ; and only their borings or tracks remain in 

 the rocks. The borings or burrows are vertical 

 in the beds, and generally in pairs, in accordance 

 "with the habit of the boring sea-worm, of sandy 

 or muddy sea-shores. The genus to which the 

 common kind is referred is called Scolithus (from 

 the Greek for worm stone). Some of these bur- 

 rows, of a kind common in the Potsdam sand- 

 stone, are represented in Fig. 265. The species 



of the St. John beds have not been particularly described. 



Trilobites * are very numerous in rocks of the Acadian epoch, as 



Fig. 247, Bryozoan (?). 

 248-250, Brachiopods : 

 248, Lingulella Mat- 

 thewi : 249, Discina 

 Acadica ; 250, Orthis 

 Billingsii. 



Fig. 254. 



heimia, Terebratella, Megerlia, Kraussia,* Bouchardia,* Morrisia, Argiope; in the 

 Thecidium family, Thecidium; in the Rhynchonella family, Rhynchonella; in the 

 Crania family, Crania; in the Discina family, Discina; in the Lingula family , Lingula. 

 There are no living species of the Orthis, Productus, and Spirifer families.' Calceola 

 (Fig. 242) is not now regarded as a Brachiopod. 



1 The genera are distinguished mainly by the form and markings of the head and 

 tail portions, and the form and position of the eyes. The large anterior segment is t}\e 

 head or buckler; the posterior, when shield-shaped and combining two or more seg- 

 ments, the pygidium. The middle area of the head, which is often very convex, is the 

 glabella ; the parts of the head either side of the glabella, the cheeks; a suture running 

 from the anterior side of the eye forward or outward, and from the posterior side of the 

 eye outward (s s in the figure), the facial suture; a 

 prominent piece on the under surface of the head, cover- 

 ing the mouth, the hypostome. The eyes may be very 

 large, as in Dalmanites (Fig. 254), Phacops, and Asaphus 

 (Fig. 360), or small, as in Homalonotus ; or not at all pro- 

 jecting, as in Trinucleus (Fig. 363); and may also differ 

 in position in different genera. 



The o-labella may be broader anteriorly, as in Phacops, 

 Dalmanites, Trinucleus; or broader posteriorly, as in Caly- 

 mene (Fi,"-. 361), Bathyurus (Fig. 301); and it may vary 

 otherwise in form ; or it may be ill defined, as in Asaphus 

 (Fig. 360) and Illmnus (Fig. 393). It may have no fur- 

 rows across its surface, or one or more up to four (or 

 rarely five). The four may be numbered^ beginning be- 

 hind^ No. 1, 2, 3, 4 (Fig. 254). These furrows may 

 extend entirelv across, or be divided at middle as Nos. 2, 3, 4. Asaphus (Fig. 360) and 

 Illmnus (Fig 393^ have none of these furrows ; Trinucleus (Fig. 363) has No. 1 faint or 

 obsolete; Asaphus (Fig. 360), Homalonotus, and Bathyurus have No. 1 entire; Dicello- 

 cephalus (Fig. 268) has Nos. 1 and 2 entire, and 3 divided; Calymene (Figs. 167, 361), 

 Dalmanites, ^Cryphem, Ogygia, Ceraurus, Proetus, have No. 1 entire, and 2, 3, 4 divided, 

 but 4 is sometimes obsolete. Sao (Fig. 281) has No. 1 entire, and 2, 3, 4 divided; but 

 there is a median longitudinal depression in which 2, 3, 4 from either side coalesce. In 

 one group, the genus Lichas, the glabella has, on either side, one or two longitudinal or 



Dalmanites Hausmanni. 



