SUB-ORDER A 



YKIt.MKS 253 



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

 monly they arc 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 are cemented together by a glutinous secretion from large glands. Fossil 

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

 rocks as old as the Ordovician. Only a few of the more common examples 

 can be mentioned here. 



Serpula, Lin. (Fig. 403). Under this head are included the majority of 

 fossil Tubicolar Annelides. 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 Palaeozoic era; but from the Jura onward, 

 numerous forms are met with, the usual condition being parasitic upon, other 

 fossils. Notably in the Lower Cretaceous their gregarious masses form beds 

 of considerable thickness (Serpulitenkalk of 

 Braunschweig, Serpulitensand of Bannewitz, 

 near Dresden). S. spirulaea, Lam. (Fig. 403 H) 

 is an abundant and characteristic Eocene 

 species. Living Serpulas have a world-wide 

 distribution. 



Terebella, Cuv. (Fig. 403 /). Cylindrical, 

 elongate, more or less bent tubes, composed 

 of cemented grains of sand or other adventi- 

 tious particles. Lias to Recent. 



Spirorbis, Daudin (Microconchus, Murch.), 



(Fig. 404). Minute, snail-like, or spirally FIG 4Q4 



enrolled calcareous tubes, cemented by the SpirorMs omplialod ^ Gom . sp . Tubes at- 

 flat under side. The spiral may be either ***! to a rooh>po<i shell (om^i,,^ 



r . J umbraculum). Devonian ; Gerolstem, Eifel. 



dextral or smistral, and is usually orna- 

 mented externally with concentric striae or annulations, sometimes with 

 tubercles or spines. Abundant in the Palaeozoic formations from the 

 Ordovician onward, and also at the present day ; somewhat less common 

 in the Mesozoic and Cenozoic eras. Living species usually adherent on 

 seaweeds. 



The following genera are commonly regarded as Annelides, but their 

 position is doubtful : 



Serpulites, Murch. Very long, smooth, compressed, and somewhat bent 

 calcareous tubes, the layers admixed with organic substance. Silurian. 



Cornulites, Schloth. Thick -walled, trumpet -shaped tubes, closed at the 

 lower end, and sometimes attaining a length of three or four inches. Exterior 

 annulated, and covered with very fine longitudinal striae. Ordovician to 

 Devonian. 



Ortonia, Nich. Small, conical, slightly flexuous, thick-walled calcareous 

 tubes, cemented by the whole of one surface to some foreign body. Sides of 



