312 



ANNULOSA. 



Fig. 182. Conchicolites gregarius, growing 

 upon the shell of an Orthoceras. Lower 

 Silurian. (Original.) 



clustered tubes growing attached to dead shells in Lower 

 Silurian strata. As in Cornulites, the tube of Conchicolites 

 appears to have been calcareous, but it is comparatively thin, 



and has none of the vesicular 

 structure so characteristic of 

 the former. The tube of 

 Conchicolites is made up of a 

 series of short conical rings, 

 inserted into one another in 

 an imbricated manner, with 

 their broader ends turned 

 away from the mouth of the 

 tube. It is worthy of notice 

 that the casts of Conchicolites, 

 from their possession of the 

 above structure, exhibit a 

 close resemblance to the 



shells of the Silurian genus Tentaculites ; whilst casts of 

 the shells of some species of the latter are absolutely un- 

 distinguishable, if fragmentary, from casts of the tubes of 

 the former. This is a remarkable fact, since Tentaculites 

 has often been regarded as a genus of Tubicolar Annelides ; 

 but there are strong reasons for believing that it is truly 

 referable to the Mollusca, and belongs to the order of the 

 Pteropods. 



Another remarkable genus is Ortonia (fig. 183), which 

 ranges from the Silurian to the Carboniferous. In this genus 

 the tube is calcareous, and is adherent along one side to a 

 shell, coral, or other foreign body. By this fact, it is dis- 

 tinguished from Conchicolites, which is only attached by the 

 lase of the tube, and is otherwise free. Moreover, in the 

 latter the tubes are clustered and gregarious, whereas those 

 of Ortonia, though frequently found in numbers attached to 

 the same shell, are always individually quite separate. The 

 tubes of Ortonia (fig. 183, B) are conical in shape, straight or 

 slightly curved, ringed with imbricating annulations, and 

 either compact or exhibiting an apparent development of 

 a cellular structure on the free surface, similar to that pres- 

 ent in Cornulites. Though with a wide geological range, 



