198 



Mcastiremciits. 



II. 



Length of tbo basioccipital to tbo cuil of tbo muscular foranicu 0.077 



Length of the hyomanilibular -. 0. 2G0 



Lcusth of tbo inferior quadrate (obliquct) 0. 11:5 



Leugtb of tbo condyle of tbo inferior quadrate 0. 03G 



Length of tbo preoperculum jireservcd 0.305 



A portion of one of the flat unsegmented or ventral spines preserved 

 exhibits an irregular rabbet on each edge of one side; width, 0"\042. The 

 sclerotic bones are as already described. 



A second specimen is still stouter in proportions, as the following meas- 

 urements show : 



Measurements. 



M. 



Diameter of tbo maxillary condyle 0.034 



Diameter of the maxilla above, bobiad the condyle 0.033 



Length of the angle of the jaw (exteriorly) 0. 050 



Diameter of tbo paraspbenoid at the middle of the prootio 0. 03 



Diameter of the dorsal vertebra (crushed) 0. 0G7 



The diameter of the vertebra must be corrected by a little reduction. 



The largest fish-vertebrae I obtained may be here mentioned. They are 

 peculiar in having numerous concentric grooves on the articular faces, as in 

 Ischi/rhiza. They are otherwise as in this genus. Length, 0".04 ; diameter, 

 0".062. 



. A peculiarity of dentition is observable in the two specimens first 

 described, and in less degree in P. molossvs. A considerable number of 

 alveolas support no functional teeth (though included in our enumeration), 

 but arc occupied at some point by successional teeth. In some cases, the 

 mouth of the alveolus appears to be narrowed by ossification, even where the 

 tip of the young tooth is in sight; in one case, so tar developed as to close up 

 to the projecting apex. In other cases, the orifice is entirely stopped by the 

 ossification, which presents the appearance of a scar with radiating lines of 

 pores. 



The first specimen was discovered in a denuded area among the lower 

 bluffs of Butte Creek. The flat cranial and jaw-bone occupied the summit 

 of a cone of twenty or more feet in height, a relic of the ancient blue lime- 

 stone strata spared from the surrounding denudation. The flat bones had 

 shed oflT the water, which, running off on all sides, had formed the cone. 



Tii(! second specimen ca IVom Fossil Spring Caiion, near the remains of 



Platecarpus curtirostris. 



