100 CARBONIFEROUS CEPHALOPODA OP IRELAND. 



no vestige of the ornaments of the shell (loc. cit., figs. 11, 12). He describes the 

 umbilical perforation in this species as " very large," though " the size could not 

 be exactly ascertained, owing to the breaking out of part of the youngest whorl." 

 In T. Hyattl, as indicated above, the central vacuity of the umbilicus is small. I 

 observe, however, that in T. Kentuchiense the central vacuity is represented in one 

 of the specimens figured (fig. 12) as very much smaller than in another (fig. 14). 

 Thus fig. 12 represents a shell resembling T. Hyattl, in this respect, as closely as 

 need be. 



Professor Hyatt does not describe the ornamentation of T Kentucldense in 

 detail, but he refers to the figure of another species {T. dejpressum), the ornamen- 

 tation of which is presumably essentially similar to that of the first-named species. 

 In his description of T. depressum he says : " The larger ridges have fine longi- 

 tudinal ridges between them, and in the later stages these become more prominent 

 and visible to the naked eye. There are usually three or four of these between 

 each pair of large ridges on the umbilical zone, where alone they were observed, 

 the condition of the shell elsewhere not permitting them to be seen. Between 

 each pair of these secondary ridges there appears, under the magnifier, a third 

 series of single longitudinal lines. Sometimes these three kinds of ridges were 

 all of the same size in the shell examined, so that it was difficult to decide 

 whether they did not all belong to the same system. The longitudinal system of 

 ridges are crossed by obscure strige of growth visible only under a magnifier in 

 this shell." 



The ornamentation here described agrees perfectly with that of the present 

 species, except that the interstitial ridges are more numerous in Hyatt's species 

 than in the latter, a difference which may well be due to the much larger size of 

 the Texan forms admitting of such additions. As regards the septation, the 

 backwardly directed sinus upon the peripheral area in T. Kentuchiense is much 

 deeper than in T. Hyatti. It may be here mentioned also that the outline of the 

 periphery is more rounded in the former species than in the latter. 



Remarks. — The most striking feature in the present species is the beautiful 

 system of ridges which so completely covers, while it ornaments, the shell. By 

 means of the sculpture the most imperfect specimens of this species may be 

 recognised, its characteristic appearance appealing at once to the eye. 



Locality. — St. Doulagh's, county of Dublin. 



