164 Mr. T. Attliey on Anthracosaurus Russelli. 



cavity ; the offsets from this are the pulp-cavities of the tooth- 

 lets ; the part between the extremity of the offset and the 

 exterior of the tooth, consisting of radiating tubules and im- 

 bedding dentine, forms the crown of the toothlet ; whilst the 

 fangs are formed by the sides of the offset of the pulp-cavity — 

 that is, by one half of a sinuous tract of light dentine,?,(the 

 narrow, dark, granular, infolded band indicating the line of 

 separation between the toothlets, or their line of union, accord- 

 ing to the view taken of the matter. 



Of these toothlets there are about twenty-four, large and 

 small together ; and their crowns form the ridges seen on the 

 exterior of a tooth. 



In Loxomma the dentinal tracts or plicse are much less 

 tortuous than the corresponding parts in Afitkracosaurus ; but 

 the infolded band, which is dark in the latter, is light in the 

 former. 



The arrangement of a compound tooth is really the same 

 in both these animals. Enamel is visible ; but certainly none 

 is infolded into the plicai or elsewhere. No cementum is any- 

 where visible. 



In my cabinet, the following separate bones of Anthraco- 

 saurus from our coal-shale, and not already noticed, occur : — 



One right maxilla. — This lies in the matrix with its inner 

 surface exposed, and measures 8^ inches in length by 1^ inch 

 in breadth at 3| inches behind its anterior end ; from this 

 point it diminishes slightly forwards, but much more rapidly 

 backwards. It bears 19 teeth, all of which are perfect and, 

 with the exception of the last, measure | inch in length from 

 the base at the alveolar border to the apex. They are oval at 

 their base in the transverse direction of the jaw, in which they 

 are arranged as follows : — The first four are placed at a short 

 distance behind the anterior end, and are in contact with each 

 other ; the fifth is y% inch behind the fourth, and the like dis- 

 tance in front of the sixth and seventh, which are in contact 

 with each other ; ^ inch separate the seventh from the eighth, 

 which is the same distance in front of the ninth, tenth, eleventh, 

 and twelfth, which are in contact with each other ; after an in- 

 terspace of y^o" inch come the thirteenth and the other six, 

 which are all nearly \ inch apart from each other. Their sur- 

 faces appear to be eroded, which gives to the teeth a ridged 

 appearance. The seventeenth tooth has been extracted ; and 

 the microscopic sections represented on Plate XI. figs. 1, 2, 3, 4 

 were made from it. 



One qiiadrate-jugal hone^ in a good state of preservation, 

 showing both its surfaces. The upper surface shows the deep 

 depression or mucus-groove along its outer margin, as figured 

 in Plate VIII. fig. 1, also the tubercle with the line from it 



