126 NEW YORK STATE MUSEUM 



The correctness of our interpretation of the groove in question is clearly 



established through comparison with Protopterus and Lepidosiren.' Only 



in one respect is there a marked distinction between the mandibles of 



Dinichthys and those of Coccosteus ; no species of the former genus are 



known to have denticulations along the symphysial margin. On the other 



hand, a series of tubercles is sometimes present along the outer face of the 



vomerine teeth in Dinichthys, and this fact suggests the probability of 



tubercles or denticles having been present in the lower dental plates as well, 



at an earlier period in the history of these forms. The differences between 



Dinichthys and Titanichthys will be considered in the discussion of the 



latter genus. 



Dinichthys halmodeus (Clarke) 



Plate 2, figure 7 ; plate to, figure i ; text figure 24 



1894 Coccosteus (?) halmodeus J. M. Clarke. N. Y. State Geol. Rep't 1893, 

 i: 162, pi. I 



1900 Dinichthys halmodeus C. H. Eastman. Jour. Geol. 8: 34 



1906 Dinichthys halmodeus Z. Hiissakof. Am. Mus. Nat. Hist. Mem. 9, 

 p. 140, text fig. 22C, 24A. 



A primitive species of small size, the head shield having a total length 

 of about 1 1 cm, and very similar to Coccosteus in the configuration of 

 plates, arrangement of sensory canals, and character of the superficial 

 ornamentation. The suture lines, however, are less undulating than in 

 Coccosteus, the articulation with the abdominal armor is ijiuch stronger, 

 the pineal is partly in contact with the centrals, and the dentition is char- 

 acteristically Dinichthyid, with strongly developed vomerine teeth. The 

 anterior margin of the lower dental plates is developed into a prominent 

 beak, and the superior or functional margin is strongly denticulated ; the 

 posterior extremity of the splenial is broad and spatulate. The suborbitals 

 are unusually wide and massive, and the rostral seems to have been laterally 

 expanded in front. The dorsomedian bears the usual inferior keel, its 



' Wiedersheim, R. Morphologische Studien. Heft i, p. 55, pi. 2, fig. 3, 8. Jena. 

 1880; Fiirbringer, K. op. cit. p. 481, pi. 39, fig. 28; Bridge, T. W. Morphology of the Skull 

 in Lepidosiren. Zool. Soc. Trans. 1898. 14:342, pi. 28, fig. 7, 8. 



