CLASS I CHAETOPODA 137 



TFiwaxia, Pollingeria and JForthenella. Typical examples of these Annelids are 

 shown in Figs. 214-16. Protoscolex and EotropJionia Ulrich, from the Eden 



Fig. 217. 

 Gephyrean Annelid, Pikrda gmcUcni' Walcott. Middle Cambrian ; British Columbia, x 2/j (from Walcott). 



shale of the Ohio Valley, are probably Ordovician representatives of this 

 order. 



Order 2. TUBICOLA. (Sedentaria.) 



Poh/chaetous Annelids ivith indistinctly separated head, and short, usually non- 

 protrusihle proboscis, without jaws. Parapodia short, and never used for swimming. 

 Inhabiting more or less firm tubes, which they construct, and subsisting ypo7i vegetable 

 matter. 



The Tubicolous Annelids invest themselves with a protective tube of more 

 or less irregular form, to which they are not organically attached, and within 

 which they can move freely. Sometimes the tubes are free^ but more com- 

 monly they are attached to foreign objects, either by the apex or by one side, 

 and may occur either singly or in clusters. The tubes frequently consist of 

 concentric layers of lime -carbonate, with vesicular cavities between the 

 lamellae, or the latter may be traversed by fine tubuli. In other cases the 

 tubes are composed of agglutinated grains of sand and other foreign particles ; 

 or they may be membranaceous or leathery. The materials for constructing 

 the tubes are procured by the tentacles or branchial filaments of the head, 

 and arc cemented together by a glutinous secretion from large glands. Fossil 

 worm-tubes are by no means of infrequent occurrence, and are known from 

 the Ordovician onwards. Only a few of the more common examples can be 

 mentioned here. 



Serpula Linn. (Fig. 218). Under this head are included the majority of 

 fossil Tubicolous Annelids. They build firm, irregularly contorted, sometimes 

 spirally enrolled, free or adherent calcareous tubes, which are frequently 

 clustered together in large numbers. Beginning in the Silurian, they are 

 sparsely represented in the Paleozoic era ; but from the Jura onward, numer- 

 ous forms occur, the usual condition being attached upon other fossils. 

 Notably in the Lower Cretaceous their gregarious masses form beds of con- 

 siderable thickness (Serpulitenkalk of Brunswick, and Serpulitensand of 

 Bannewitz, near Dresden). S. spirulaea Lam. (Fig. 218, H) is an abundant 

 and characteristic Eocene species. Eecent Serpulas have a world - wide 

 distribution. 



