56 Prof. H. A. Nicholson — On Fossil Tuhkolar Annelides. 



spaces. None of tlie tubes are perfectly straight, but all are more 

 or less curved, especially towards their attached ends. The extent 

 of the attached portion of the tube varies, being mostly from one to 

 two lines. Their unattached portions run generally (in any two 

 contiguous tubes) more or less nearly parallel to one another ; but, 

 though in contact in many instances, it is doubtful if they are 

 actually adherent, and they are most probably not so. 



From Conchicolttes gregarius, the present species is distinguished 

 by its greater average length and much greater diameter, by its 

 much less closely crowded habit, and by its much more strongly 

 marked annulations. 



Log. and Form. — Attached to the shell of Cyclonema (Pleuro- 

 tomaria) hilix, Conrad, from the Hudson Eiver Group (Lower 

 Silurian) of Cincinnati, Ohio. 



Ortonia minor, Nich. — Spec. Char. Tube calcareous, solitary, 

 attached by the whole of one side to some foreign object. Length of 

 tube from -^'q. to -^-^ of an inch ; diameter at mouth from -^L- to -^^j- of 

 an inch. Tube marked with transverse ridges or annulations, which 

 are sometimes faintly marked on the side opposite to the attached 

 surface, and the number of which is about fifteen in a tenth of an 

 inch. Tube in general strongly curved towards its smaller extremity 

 (Plate IV. Fig. 3). 



Numerous specimens of this very distinct species have been placed 

 in my hands by Professor Orton and Mr. U. P. James of Cincinnati. 

 They occur growing upon valves of StropTiomence, Ortliis plano- 

 convexa, Hall, and other Brachiopods ; and I have also a fragment of 

 Chcetetes lycoperdon, Lay, covered with these little tubes. There can 

 be no doubt as to the correct reference of this species to the genus 

 Ortonia, which I recently proposed (Geological Magazine, Vol. IX. 

 p. 446) for another Tubicolar Annelide from the same horizon. The 

 only point in which it does not agree with the character which 

 I proposed for Ortonia, is that it does not appear to have any 

 cellular structure of the tube. In Ortonia conica, however, this 

 cellular structure is confined entirely to a small portion of the tube 

 (namely, to that portion opposite to the attached surface), and the 

 absence of even this in the present species shows that it cannot be 

 regarded as a generic character. The only approach to the same 

 structure which I can detect in Ortonia minor is that the transverse 

 rings or annulations which surround the tube become faint or 

 obsolete on the side opposite to the attached surface. Even this, 

 however, is by no means constant, and the rings are sometimes 

 completely continuous over the whole unattached surface of the 

 tube. 



Though often occurring in great numbers together, the tubes of 

 Ortonia minor, like those of Ortonia conica, are strictly speaking 

 solitary ; that is to say, they do not, like the tubes of Serpula or 

 Conchicolites, interfere with one another or come into contact except 

 accidentally. The tube is generally pretty nearly circular in section, 

 though sometimes slightly trigonal, conical, and always more or less 

 curved. Sometimes it is simply curved like a horn ; sometimes it is 



