SUB-ORDER A VERMES PAs} 
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 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 J). 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 
enrolled calcareous tubes, cemented by the  gyinorbis omphalodes, Goldf, sp. Tubes at- 
flat under side. The spiral may be either tached to a Brachiopod shell (Orthothetes 
aes S umbraculum). Devonian; Gerolstein, Eifel. 
dextral or sinistral, 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, 
LLL) 
S) 
S 
“Li 

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 
