FISH-REMAINS OF THE CARBONIFEROUS ROCKS. 89 



(ins tooth, cut iu longitudinal section, exhibits the almost 

 parallel vascular canals running perpendicularly to the sur- 

 face. The interspaces are about six times the diameter of 

 the tubes. From them there proceed the extremely fine 

 branching dentinal tubules before mentioned, which traverse 

 the interspaces of calcified tooth-substance in fine, wavy, den- 

 dritic lines. In this tooth the passage from crown to root 

 appears more abrupt than it is in Orodus^ Psepliodus^ or 

 Hclodits. In a section of the tooth of Pseplwdus the vascular 

 canals, as they approach and pass into the base of the tooth, 

 become wavy and coiled, pursuing a sinuous course. In one 

 slice of Ovodus the minute structure is well shown, and the 

 relation of the red staining material (presumably some iron 

 compound) to the canals is well shown. The lumen of the 

 tube is bordered by a lighter, clearer band, in which and 

 through which the dentinal tubules branch out. Into this 

 band, and sometimes beyond it, the red material, which is 

 perfectly translucent nnder the microscope, has passed ir- 

 regularly by infiltration. The edge of the stained part there- 

 fore presents an irregular mammillated wav}^ or sinuous 

 curve. In none of our transverse sections do we find definite 

 indications of concentric lamellse like those of the Haversian 

 canals in bone. 



We pass now to a brief notice of the ichthyodorulites, or 

 fish-spines. 



Certain laterally compressed, robust, and often large 

 spines have been found in the Bristol rocks. They are 

 generally marked by ridges extending from the j^ointed end 

 to within a short distance of the more rounded extremity. 

 Small denticles, or wrinkles, appear between these ridges. 

 The spine seems to have been sharp in front, while the 

 hinder part was concave or flat, with small tooth-like excres- 

 cences along each margin. They go by the generic name of 



