POLYCH/ETA. 



477 



ambulations, and the free surface of the tube, in some species, appears 

 to have a cellular structure, similar to that which is seen in the tube 

 of Cornulites : but the microscopic characters of Ortonia have not 



Fig. 341. — A, Tubes of Ortonia conica growing upon the valve of Strophomena alternata, 

 natural size; b, A single tube of the same, enlarged. Ordovician. (Original.) 



as yet been worked out. The known species of Orto?iia are found 

 in the Ordovician, Silurian, Devonian, and Carboniferous rocks. 

 It may be noted in this connection that the tubes of some species 

 of Ortonia, except for being attached along one side to foreign 

 bodies, present a considerable 

 general likeness to the tubes of 

 the genus Tentaculites, which 

 genus high authorities have re- 

 garded as Annelidan. There 

 are, however, important distinc- 

 tions between these two types, 



! 



and the genus Tentaculites will 

 be considered here under the 

 Pteropoda, to which group, in 

 the author's opinion, it is pro- 

 perly referable. 



A Similar Superficial likeness F ig- 3^.—Conchicolites gregarius, growing 



. . i-i-ii upon the shell of an Orthoceras. Ordovician. 



to Tentaculites is exhibited by (Original.) 

 the Ordovician genus Conchico- 



lites, which is certainly Annelidan. In this genus (fig. 342) the 

 animal was social, and formed masses of clustered tubes, growing 

 side by side, attached by their bases to the outside of the dead 

 shells of Orthocerata or Brachiopods. Each tube is made up of 

 short imbricating rings, each of which partially overlaps the one 

 below. Hence the cast of the tube (the right-hand figure in fig. 



