Eastman — Dipnoan Affinities of Arihrodires. 137 



worked out for a new genus, intermediate between Mylostoma 

 and Dinichthys — as the name D in omylo stoma implies — from 

 the Portage beds of Mt. Morris, New York. For the privi- 

 lege of studying the important specimen referred to, the writer 

 is indebted to his friend Professor Schuchert, of Yale, in 

 whose custody it is, and at whose suggestion the specific title 

 is inscribed to the memory of the late Professor Beecher. 



It is beside our purpose to present here a detailed account 

 of the new form ; suffice it to note that it permits accurate 



Fig. 2. — External aspect of (a) right, and (b) left mandibles of Diaomylo- 

 stoma beecheri (MS.), from the Portage of western New York, x %. 



reconstruction of the entire dental apparatus, and acquaints us 

 for the first time with the articular union between the lower 

 jaw and cranium of Arthrodires. In this latter respect the 

 conditions are exactly as we should anticipate from analogy 

 with Neoceratod.us / the articular cartilage is attached to the 

 outer surface of the splenial at its posterior extremity, and 

 forms a hinge with the suspensorial cartilage of the cranium. 

 Whether this latter was in direct connection with the head- 

 shield, or supported by a squamosal element, we are as yet with- 

 out information. The articular cartilage of the left mandible 

 is somewhat indistinctly shown in text-figure 2 ; that belong- 

 ing to the right mandible is removable, and has been omitted 

 in the uppermost figure. 



Am. Jour. Sci.— Fourth Series, Vol. XXI, No. 122.— February, 1906. 

 10 



