GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 343 



lOHTHYODECTES, Oope. 



Proc. Amer. Philos. Soc, 1870, Nov.; Hayden's GeoL Survey, Wyoming, &c., 1871, p. 421. 



Teeth equal, subcylindric, in a single row, sank in deep alveoli. Pre- 

 maxillaries short. No foramina at the bases of the teeth on the inner 

 alveolar walls. Vertebrae deeply grooved laterally. 



The species of this genus are, so far as known, smaller than those of 

 the last, and, as their remains are more perishable than those, form a 

 less striking object among the fossils of Kansas. They are, neverthe- 

 less, very abundant, especially in species, five of which are now described. 

 In originally describing this genus the vertebrae were regarded as not 

 grooved, in consequence of such vertebrae having been discovered along 

 with the bones and teeth of I. ctenodon. Further examination has satis- 

 fled me that this union is erroneous, and that the bones, if found 

 together, were accidentally so. 



Spines similar to those of the Porthei, but presenting certain differ- 

 ences, may be ascribed to this genus. The compound segmented spines 

 cannot be ascribed to it, but the compound fulcrum-like spines are 

 similar, though composed of fewer and stouter rods. Each of these, as 

 it terminates at the cutting edge, gives rise to a projection, giving it an 

 obtusely and remotely serrate character. It is rugose with enamel 

 deposit, and constitutes as effective a weapon of defense as that of For- 

 tlieu's. One which is nearly perfect contains fifteen pairs of rods, which 

 expand at the base as do the rays of a pectoral fin. Total length, .235 

 meter; width at base, .04 meter; thickness beyond base, .OOG meter. 



The femoral bones have already been described. The maxillary is 

 not contracted at the end for a supernumerary bone, as in Fortheus. 



The form of the inferior quadrate is like that of Fortheus. In I. 

 anaides the groove for the preoperculum extends low down, and the 

 symplectic has a wider exposure on the outer face than in Fortheus. 



In a series of vertebrae similar to those of this genus, those included 

 in the basis of the caudal fin are not more than three in number. 



The species are distinguished as follows: 



Premaxillary teeth, 5, second most prominent ; maxil- 

 lary not concave ; dentary with 30 teeth and bi- 

 convex, alveolar border, with obtuse extremity I. anaides. 



Premaxillaries; maxillary straight, large, with 40 

 teeth ; dentary straight, not produced at end ; 

 teeth, 26 J. ctenodon. 



Premaxillaries, 5, first most j)rominent ; maxillary 

 concave, narrow ; teeth small ; dentary with a hook 

 at apex ; teeth, 25 I. hamatus. 



Premaxillaries, 7, first most prominent, compressed, 



smaller 1. prognathus. 



Premaxillaries, 12, second most prominent ; the bone 

 much narrowed above, smaller J. muUidentatus. 



The Euglish species of this genus is figured by Dixon in the Geology 

 of Sussex, PL xxxii, Figs. 9 and 9*. I can find no letter-press nor 

 name relating to it, and cannot determine its specific characters from 

 the fragmentary character of the piece of mandible figured. 



SAUEOCEPHALUS, Harlan. 



Leidy has pointed out the mode of implantation of the teeth in the 

 typical species of this genus. The mode of succession of the teeth has 



