WiLLisTON.] Mosasaurs. 173 



of its vertebrae traces of a notch, which, in the latter, separate 

 the zygosphene from the zygapophyses. Unfortunately other 

 portions of the genus are unknown." 



Lesticodus was given by Leidy to a species (L. impar) repre- 

 sented by teeth and portions of the jaws, and was afterwards 

 abandoned by him. Cope evidently believed that the genus 

 was the same as Liodon Cope. 



Nectoportheus Cope was based upon Liodon validus (olim Macro- 

 saurus) and was characterized by him as follows ( Extinct Ba- 

 trachia, etc., 208) : "The posterior dorsals are so much more 

 depressed than in Liodon. Isevis, that future discovery may 

 justify the generic separation of the genus Nectoportheus, which 

 I originally applied to this animal." In his Cretaceous Verte- 

 brata (p. 160) he says: "The typical species of this genus 

 (Liodon anceps Owen) is very little known, but few remains 

 having been obtained from the English Chalk, its locality and 

 horizon. Numerous North American species resemble it in the 

 forms of the crown of the teeth, and it is probable, though un- 

 certain, that they agree in other respects also. Several names 

 have been proposed for our species, the earliest of which is 

 Macrosaurus Owen. This name applies to species with com- 

 pressed dorsal vertebra?, as L. Isevis and L. mitchelii, both from 

 the New Jersey Greensand. For species with the depressed 

 dorsal vertebrae, as L. validus from New Jersey, L.perlatus from 

 New Jersey, and L. proriger from Kansas, the name Necto- 

 portheus was proposed and briefly characterized." 



The definition of Tylosaurus (Rhinosaurus) was explicit and 



exact, leaving no doubt of the genus to which it was intended 



to apply. 



Tylosaurus proriger. 



Maorosaurus proriger Cope, Proc. Acad. Nat. Sci. Phil., 1869, p. 163; 



Ext. Batrachia, etc., pi. xn, ff. 22-24. 

 Liodon proriger Cope, Ext. Batrachia, etc., 202, Cret. Vert., 161, pi. xxvn, 



ff. 8, 9; xxx, ff. 10-13; xxxvi, f. 2; xxxvn, f. 6. 

 Rhinosaurus proriger Marsh, Amer. Journ. Sci,, June, 1872. 

 Rhamphosaurus proriger Cope, Proc. Acad. Nat. Sci. Phil., 1872, p. 41. 

 Tylosaurus proriger Leidy, Ext. Vert. Fauna West. Terr., 274, 344, pi. 



xxxv, ff. 12, 13; xxxvi, ff. 1-3. Merriam, Ueber die Pyth. der Kans.- 



Kreide, 14. Williston, Kans. Univ. Quart., vi, 98, pis. ix-xii; 107, pi. xiii ; 



177, pi. xx. 



