EASTMAN: MYLOSTOMID DENTITION. 223 



belonged to a single individual. This is shown by their almost perfect 

 symmetry, similar texture, equal extent of wear, and especially by the evi- 

 dence of co-adaptation along their linear inner margins, where they were 

 in contact along the median line. The indications of a rigid cartilaginous 

 union at the symphysis are of an even more positive character than in 

 Ptyctodonts, for in these plates the contact line is more extended, and 

 the adjustment along the vertical inner face more accurate. On bring- 

 ing these surfaces into adjustment, it is easy to see from the alignment 

 of the splenial portions that the angle subtended by the mandibular 

 rami must have been very narrow. The pointed form of the plates in 

 front leads also to the conclusion that the head was sharp-snouted, 

 slender, and elongate, indicating a creature adapted for rapid motion, 

 and possibly one having an eel-like form of body. 



A marked feature of the mandibular plates as compared with those 

 of the type species of Mylostoma is the narrowness of their functional 

 surface, with tapering forward extremities, a character by which the new 

 form is readily distinguished from all other Mylostomids. The trit- 

 urating surface is moderately convex, and displays the usual tubercle 

 along the inner margin, although this is less elevated than in other 

 species, and is more distinctly separated from the posterior portion 

 of the plate by a deep sinus. This is the concavity referred to in New- 

 berry's description, where it is suggested that the posterior margin 

 of the " premandibular " plates is "obliquely notched, apparently 

 to receive the obtuse points of the larger teeth." In addition to the 

 main eminence along the inner margin, faint indications are visible in 

 the Cambridge specimen of two or three rows of smaller tubercles, radi- 

 ating outwards in a manner strikingly suggestive of Ctenodipterine teeth. 

 Similar markings were no doubt present in the Oberlin examples as well, 

 but have become obliterated by wear. Their larger size and more worn 

 condition suggest that they pertained to an older individual than that 

 represented by the Cambridge specimen (M. C. Z., Cat. no. 1439). The 

 form of all three strongly recalls Ctenodipterine conditions, and it is 

 probable that the resemblance extended to the upper dental plates as well. 

 They were no doubt attenuated anteriorly in corresponding fashion with 

 the mandibular plates, their oral surfaces were regularly concave and very 

 possibly tuberculated, and it would not be at all surprising if the two 

 pairs of upper dental plates common to other Mylostomids were in this 

 species fused into one. This would give rise to a compact triangular- 

 shaped plate, closely paralleling those of typical Dipnoans. 



The new species may appropriately be named in honor of the memory 



