260 University Geological Survey of Kansas. 



to the jaw-bones. Abdominal vertebrae, at least, without deep lateral pits, but 

 longitudinally striated. Ex.: Pachyrhizodus, Empo (/), Stratodus. 



"III. Fishes only moderately compressed from side to side, naked, or pro- 

 vided with scutes. Both maxilla and premax'illa long and slender, the former 

 about half excluded from the margin of the upper jaw by the latter; the maxil- 

 lary and premaxillary teeth small. Palatines and ectopterygoids powerful, and 

 bearing a single series of large teeth, upon expanded, anchylosed to the bone. 

 Dentary bone of lower jaw with one series of large teeth and one or more series 

 of small teeth similarly anchylosed. Vertebrae with two deep lateral impressions 

 and pits for the neural and haemal arches. Ex.: Enchodus, Eurygnathus, 

 Eurypholis, Ischyrocephalus, Cimolichthys, Pomag -net-thus. 



"IV. Elongated fishes, with powerful dentition, and the trunk armed with 

 several longitudinal series of bony scutes; not yet precisely defined and separated 

 from groups II and III. Ex.: Dercetis {Leptotraehehts), Peldrgorhynchus, 

 Plinthophorus. 



"V. The Protosphyrcenidce (Erisichtheidce Cope), with much elongated 

 snout (ethmoid bone), and long maxilla loosely connected with the premaxilla: 

 also believed to have an unusually complex mandible. Ex.: Protosphyrcena. 



"VI. Clupeoids and salmonoids." 



t 



After making a careful study of the material at hand, I think 

 it advisable to make some changes in the above grouping for 

 the American genera, which are given below. 



I. Fishes with skull laterally compressed; jaws powerful, 

 and bearing a single row of cylindric teeth, without nutrient 

 foramen or notches below the internal alveolar border ; preden- 

 tary not present ; vertebrae deeply grooved, with pits above and 

 below for the insertion of the neuro- and haemapophyses. Em- 

 bracing the genera Xiphactinus, Icthyodectes , Gillicus, and Clado- 

 cyclus; family, Icthyodectidx. 



II. Fishes with skull laterally compressed ; jaws powerful, 

 and bearing a single row of compressed, knife-like teeth, with 

 nutrient foramina or notches below the internal alveolar bor- 

 der ; predentary present and without teeth. Including the 

 genera Saurodon and Saurocephalus ; family, Saurodontida>. 



III. Fishes with skull depressed, the top of which is beauti- 

 fully sculptured ; jaws provided with one or more series of con- 

 ical teeth, which are firmly anchylosed to the bone; vertebrae 



