EASTMAN : MYLOSTOMID DENTITION. 



215 



of the dental apparatus of Mylostoma, his interest in the problem having 

 been aroused by the discovery of a well-preserved skeleton of M. varia- 

 bile, the various parts of which obviously belonged to a single individual. 

 This specimen presented for examination the ilatteued headshield, some 

 half-dozen plates of the abdominal armor, both mandibles, and two pairs 

 of crushing dental plates, all embedded in close proximity to one another 

 in a single block of shale. Tliere were no indications, however, of the 

 presence of a fourth pair of dental elements, corresponding to the so- 

 called " premandibular teeth " of jS'ewberry, and these latter do not 

 enter into Dean's reconstruction. 



As will be seen from Figure A, which is copied from Dean, the two 

 mandibular rami were found lying nearly parallel to each other in close 



FlGUEE B. 

 Restoration of the complete dentition of Mylostoma, based upon the single individual of 

 M. variabile shown in Figure A. The length of the mandibular dental plate is slightly- 

 exaggerated in the outline here shown. X h (After Dean). 



proximity to the headshield, and at no great distance from the sepa- 

 rated halves of the palatal dentition. The two plates interpreted by 

 Dean as belonging to the right-hand side of the palate are in direct 

 apposition with each other, their contact edges being in remarkably 

 close adjustment. These circumstances, the fact that the two right- 

 hand palatal plates remain together while the corresponding left-hand 

 plates have become separated, and the fact that their opposed edges 

 show almost perfect co-adaptation, are held by Dean to point irresist- 

 ibly to the conclusion that the elements in question have preserved 

 their natural arrangement with respect to each other.^ It is not demon- 

 strated by the author, but merely considered as extremely probable that 



1 Dean, B., Palaeontological Notes. Mem. N. Y. Acad. Sci., 1901, 2, p. 104. 



