140 



ANNULOSA. 



and the little S. carbonarius (fig. 89) is a common species in 

 the Carboniferous Rocks, whilst more than one form has been 

 described from the Permian series. The genus continues to 



Fig. 89. Spirorbis (Microconchus) carbonarius ; natural size, attached to a fossil plant, 

 and magnified. Carboniferous. (After Dawson.) 



be well represented in both Mesozoic and Tertiary deposits ; 



and living forms, apparently little different from the fossil ones, 



abound in recent seas. 



The genus Scrpttla (fig. 90) possesses a long shelly tube, 



usually more or less tor- 

 tuous, sometimes solitary, 

 sometimes aggregated, and 

 fixed to some foreign body 

 by part of its surface. Spe- 

 cies of this genus have 

 been described from the 

 Upper Silurian, Devonian, 

 and Carboniferous forma- 

 tions. In the Trias some 

 species occur, and many 

 forms are known from the 

 Oolitic and Cretaceous 

 formations, whilst they are 

 equally numerous in the 

 Tertiary series. 



Of the other fossils re- 

 ferred to the Tubicolar 

 Annelides, the only one 

 which needs notice is the 

 genus Ditrupa. The tube 

 in this genus is unattached, 

 open at both extremities, 

 and very closely resem- 

 This genus does not seem to 



Fig. 90. Serpulaflagellum. 

 (Jurassic.) 



Oxford Clay. 



bling the shell of a Dentalium. 



