Cope.] 316 [February 17, 



acuminate outline. The flat anterior, inferior dentinal column is pre- 

 sent as in /. mirijicus, but is much less oblique and more transverse 

 than in the latter; the antero-inferior margin is thus broader. 



Lines. 



Length from outer posterior tubercle 39 



Depth at same point 25.5 



Greatest width at same point 19 



Length of outer anterior tubercle 4.7 



Isehyodus Smoekii Cope.^ 



This species is intermediate between the two species of the genus 

 already mentioned, and is about half the size of the smaller, /. divari- 

 catus. Several specimens of mandibular rami from the Ci*etaceous 

 Green-sand of New Jersey. * 



The general proportions are much less elongate than in the /. miri- 

 Jicus, but not so stout as in I. divaricatus. The tubercles are rela- 

 tively much larger than in either, and all with planer surfaces than 

 either ; they are therefore elevated supero-anteriorly, and the plane of 

 the posterior face descends abruptly from the supero-anterior margin 

 of each . The outer margin has therefore an outline of two steps ; the 

 inner of one. The outer tubercles are narrowed in front ; the inner 

 is more obtuse and is large, being separated by a very narrow strip 

 from the outer posterior. It is not divided into three as in /. mirifi- 

 cus ; also the small inner terminal column of that species is wanting, 

 as in /. divaricatus. It differs from the last named in its regular ex- 

 tremity, without elevated and expanded symphyseal margin. The 

 outer face is uniformly concave transversely ; the inner face has 

 also a longitudinal concavity which is much stronger. The sm'face 

 strife are longitudinal; sometimes broken. 



Lines 

 Length from anterior extremity of posterior outer tubercle ; 



(a little of apex restored.) 28 



Depth from same point 20 



Length of anterior outer tubercle 12 



Width of interior tubercle 11 



This species is dedicated to John C. Smock, assistant on the State 

 Geological Survey of New Jersey under Prof. Cook, as a recognition 

 of his labors, and material aid therein. 



Plinthieus stenodon Cope gen. et spec. nov. Myliobatidarum. 



Char. gen. Masticatory surface of the tooth in a transverse band, 

 which does not stand above the laminated insertion into the 



