448 Trof. H. A. Nicholson — Oji the Genus Ortonia. 



opens by a more or less nearly circular aperture ; and the continuity 

 of the tube, from its open to its closed extremity, is not interrupted by 

 any internal septa. The surface-characters of the tubes are of a very 

 remarkable character. Upon the surface, diametrically opposed to 

 that along which the tube is attached to the shell, the tube is of a 

 cellular character, exhibiting numerous rounded pits or alveoli, which 

 strongly remind one of the peculiar cellular structure of the tube of 

 Cornulites. This peculiar structure occupies a narrow belt running 

 down the tube, along its dorsal or free surface ; and from both sides 

 of this belt there proceeds a series of strong annular ridges or rings 

 which pass round the tube, to disappear on its fixed margin. These 

 rings are not separated by secondary intermediate annulations ; nor 

 do they exhibit any -longitudinal striation. Sections of the tubes, 

 however, show that these rings are just as visible on the interior of 

 of the tube as they are externally. 



No reasonable doubt can be maintained as to the zoological position 

 of Ortonia. It is unquestionable that we have to deal here with 

 a true Tubicolar Annelide, nearly allied to the recent Serpulce. 

 Ortonia is still more nearly related to the extinct genus Cornu- 

 lites, from which it differs in its much smaller size, and in being 

 attached along the whole of one side, instead of by its smaller 

 extremity only. It differs, also, in having the peculiar cellular 

 structure of the tube confined to a definite portion of its surface, and 

 in being altogether destitute of longitudinal striation. From Con- 

 cJiicolites, again, Ortonia is distinguished by the much more complete 

 mode of its attachment, and by the fact that the tubes are never 

 attached socially in clustered masses, growing side by side, as is the 

 case in the former genus. 



The following diagnosis gives the characters of the genus Ortonia 

 and of the single known species : — Ortonia, Nich. — Animal solitary 

 inhabiting a calcareous tube, which is attached along the whole of 

 one side to some foreign body. Tube, slightly flexuous, conical, in 

 section cylindrical, or somewhat flattened laterally, and sub-triangu- 

 lar. Walls of the tube thick, cellular along the surface opposite 

 to the attached portion, markedly annulated along the sides. 



Ortonia conica, Nich. — Tubes growing attached to the shell of 

 some Mollusc ; varying in length from :|- to -J inch, with a diameter 

 of about tV of an inch at the mouth. Lateral annulations of the 

 tube varying in number from 30 to 35 in the space of an inch. 

 Surface smooth and completely destitute, so far as observed, of 

 longitudinal striae. 



The fossil from which the above description has been taken is an 

 example of Strophomena alternata, to the dorsal valve of which are 

 attached the remains of more than twenty individuals of Ortonia 

 conica. In one case the tube of one crosses that of another indi- 

 vidual ; but it is quite clear that this is an accidental circumstance, 

 so to speak, and that the tubes are truly solitary. The specimen is 

 from the " Cincinnati group " of South-Western Ohio, a formation 

 which belongs to the "Hudson Eiver series," and which corresponds 

 with the Caradoo or Bala division of the Lower Silurian. 



