222 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



into Dean's restoration of the Mylostomid dentition, nor is their exist- 

 ence mentioned. As a matter of fact, the actual specimens had been 

 lost sight of for many years, and in the absence of satisfactory illustra- 

 tions it was difficult to hazard a conjecture as to their nature. Without 

 having studied the originals, no one could have concluded that they had 

 suffered such injury as to obscure their real nature, nor could any good 

 reason be assigned for excluding them from association with the type 

 species of Mylostoma. 



By a fortunate chance the original pair of Newberry's so-called " pre- 

 mandibular teeth " have been preserved intact in the Museum of Oberlin 

 College, where they were overlooked until recently. Being recog- 

 nized by Dr. Hussakof, after searching various collections, they were 

 loaned to him and subsequently placed in the hands of the present 

 writer for purpose of further study and description. Grateful acknowl- 

 edgments are hereby rendered to the writer's colleagues in New York 

 and Oberlin for having thus provided an opportunity for the following 

 observations. 



Comparison of the original pair of dental elements figured in Plate 16, 

 Figure 4, of Newberry's Monograph with the lower dental plates of Mylos- 

 toma, especially those of the single individual of M. variabile described 

 by Dean, leaves no room for doubt that they are of similar nature. We 

 have not to do with integral paired structures representing a distinct 

 element, but with a fractured pair of mandibles belonging to a new 

 species of Mylostoma. The inferior aspect in particular of Newberry's 

 originals displays the usual conformation of grooves, ridges, and hollows 

 with which we are familiar in Mylostomid mandibles. One of these 

 grooves is extremely characteristic of the Arthrodiran type of mandible, 

 always occupying the same position, and from its similarity to a corre- 

 sponding groove in modern Dipneumoni, has been interpreted as serving 

 to lodge remnants of the Meckelian cartilage. The line of fracture along 

 which the posterior shaft of the splenial has been broken off is irregular, 

 even ragged in places, and so obviously the result of injury that it is 

 surprising Newberry should not have noticed it. Curiously enough, in 

 the case of the solitary known specimen agreeing with the typical pair, 

 the same which we have previously called " vomerine," signs of injury 

 are scarcely to be perceived, and would seem to have become almost 

 wholly obliterated by post-mortem attrition. Yet it follows by implica- 

 tion that the Cambridge specimen has likewise suffered the loss of the 

 supporting splenial. 



There can be no question that the Oberlin pair of mandibular plates 



