PALEOZOIC TIME — LOWEE SILURIAN. 



51^ 



721. 



and Upper Group ; and the Christiania district, a Lower Group of Grapto- 

 litic shales with sandstone, and an Upper, consisting largely of limestone 

 with some shales. 



LIFE. 



Plants. — The figure here given has great interest on account of its 

 representing a specimen of a Lower Silurian plant above the level of a sea- 

 weed. It is from the Skiddaw slates. A. Nicholson, the discoverer, described 

 it as a seaweed (ButhoPrephis Hark- 

 nessi), and this it may still be. But 

 Dawson refers it, with reason ap- 

 parently, to the Marsileaceae, — at 

 present fresh- water plants of the higher 

 Cryptogams. As the group of leaves 

 xesembles the whorl on the stem of an 

 Eqnisetum, he named the genus Protan- 

 nidaria, the name implying a relation 

 to the genus Annularia of this tribe. 



Animals. — The following are 

 figures of a few other fossils. Ortliis 

 flabeUulum(Fig. 722) occurs in the Bala 

 limestone. Ortliis elegantida (Fig. 723) 

 ranges from the middle of the Lower 

 Silurian (Coniston limestone) to the 

 Wenlock of the Upper Silurian. The 

 Crania (Fig. 724) is from the Bala. 

 Asaphus Powisi (Fig. 726) and Ampyx 

 midus (Fig. 728) are Llandeilo Trilo- 

 bites, and lUcenus Davisi (Fig. 727) 

 ■occurs in the Bala limestone. 



Fig. 729 represents the telson or caudal segment and appendage of a large 

 Ceratiocaris, C. Angelini, from the upper member of the Lower Silurian in 



722-728. 

 726. 



Protannularia Harknessi. 



iEACHioPODS. — Fig-. 722, Orthis flabellulum ; 723, O. elegantula; 724, Crania divaricata. Lamellibraijch. — 

 725, Conocardium dipterum. Tkilobites. — 726, Asaphus Pomsi ; 727, lUaenus Davisi ; 728, Ampyx nudus. 



Sweden. The length of this Crustacean in its entire state must have been 

 fully one foot. 



