CLASS II 



GEPHYREA 



141 



Fig. 224. 



Nereites camhrensis M'Leay. Cambrian ; Llampeter, Wales. 

 Natural size. 



Olass 2. GEPHYREA. 



Marine Annelida without parajpodia and typically devoid of any trace of 

 segnientation in the adult condition. 



The Cambrian genera referred to this class by Walcott differ in certain 



respects from the Kecent members, but with our available information the 



Position here assigned them 



seems most advisable. Two 



f amilies, (1) Ottoidae, with the 



genera Ottoia and Banffia, and 



(2) Pikaidae, including Pikaia 



(Fig. 217) and Oesia, all from 



the Middle Cambrian of British 



Columbia, are recognised. 



A quantity of supposed 



worm-borings, trails, impres- 



sions and otherobscureremains 



have been described from the 



older Paleozoic formations. 



The burrows have the form 



of straight or tortuous tunnels, 



and are sometimes hollow, 



but more commonly have been 



filled up by solid matrix. Various names have been applied to them, 



such as Scolithus, Arenicola, Histioderma, Planolifes, Diplocraterion, Spirocolex, 



Scolecoderma etc., but they are obviously incapable of precise determination. 



Arthrophycus Hall, originally described as a plant, Daedalus (including Vexillum 



Roualt) and Taonurus Fisher- 



^^'<i4. '''^!^^z^st^^^is^^^^^:^ Ooster (Spirophyton Hall), have 



in recent years been interpreted 

 as worm burrows. • 



Similarly, the Serpentine or 

 vermiform impressions known as 

 Nereites, consisting usually of a 

 number of windings, and often of 

 profuse occurrence in various 

 Paleozoic formations, were until 

 quite recently regarded as worm- 

 trails, or markings made by 

 Fucoids. These also have re- 

 ceived . numerous appellations, 

 such as Nereites (Fig. 224), N'e- 

 mertites, Myrianites, Nemapodia, 

 Crossopodia (Fig. 225), Phyllodo- 

 cites, Naites, etc. Nathorst, how- 

 ever, has brought forward ex- 

 perimental evidence to prove that the majority of these markings have been 



produced by the movements of Crustaceans, Annelids and Gastropods. A like 



origin may reasonably be ascribed to the extraordinarily abundant and variable 



FifJ. 225. 



CrossopoiUa (Crossochorda) scotica M'Coy. Ordovician 

 IJagnoles, Norniandy. 



