Vrof. H. A. Nicholson — On the Genus Ortonia. 447 



proposed the genus ConcMcoUtes, to include Tubicolar Annelidas, the 

 tubes of which are attached socially in clustered masses to dead 

 shells. The tubes are composed of short imbricated rings, and are 

 ranged side by side, being attached by their smaller ends only. The 

 genus is, so far as known, confined to the Lower Silurian rocks ; 

 and broken fragments are almost, or quite, undistinguishable from 

 Tentaculites (American Journ. Science and Arts, vol. iii., no. 15, 1872). 

 I have now to found another genus for the reception of an 

 allied but very distinct Tubicolar Ann elide, which has been pre- 

 viously referred with doubt to Tentaculites. This genus I propose to 

 name Ortonia, after Mr. Edward Orton, of the Geological Survey of 

 Ohio, who has kindly furnished me with specimens. Only a single 

 species is known to me, from the Lower Silurian (Hudson Eiver 

 group) of South-Western Ohio, where it appears to be a common 

 fossil. It has been doubtfully identified with Hall's Tentaculites 

 flexuosa (Pal. New York, vol. i. p. 92) ; and if this determination 

 could be relied upon, I would gladly retain the above specific name. 

 Hall, however, describes his species as being furnished with distinct 

 internal transerve septa ; and this structure is certainly altogether 

 wanting in our fossil. I shall, therefore, adopt for the present form 

 the name of Ortonia couica, in allusion to the form of the investing 

 tube. 



A. B. 



Fig. 1.— a. Tubes of Ortonia conica, Nich., growing upon the valve of Strophomena 

 alternata. Nat. Size. B. A single tube of tlie same, enlarged. 



The genus Ortonia comprises small conical calcareous tubes, which 

 are found attached to the outer surfaces of the shells of Brachiopods 

 or other Molluscs. Mr. Orton informs me that in one locality, at 

 Cincinnati, the species confines its parasitism entirely to Strophomena 

 alternata ; but elsewhere it attaches itself to other shells as well. 

 The tubes are attached along the whole of one side, full-grown 

 specimens being from four to sixth-tenths of an inch in length. In 

 shape, the tubes are markedly conical (Fig. 1b), their section being- 

 circular, or at times somewhat trigonal. Almost all the tubes, 

 though in the main straight, are more or less cui-ved and bent towards 

 their smaller closed extremities. The widest extremity of the tube 



