160 GEOLOGY AND PALEONTOLOGY. 



heiglit and width, carinated and nodo-costate ; dorsal carina continuous, the approximate series 

 of tubercles not equal to it in prominence; ribs numerous, 22 on each volution, equidistant, 

 ornamented with 5 tubercles ; series near the dorsal carina compressed, elongated, the others 

 rounded ; transverse section of the exterior volution rectangular, of the interior volution quad- 

 rate ; sutures of septa moderately divided and ramose. 

 Locality. — Near Puercos river. 



AMMONITES LEONENSIS. 



Plate XVI, Fig. 2, a, h. 



Volutions with thick, distant, rounded ribs, with a tubercle on each extremity and an inter- 

 mediate rudimentary rib, having a tubercle on the dorsal angle ; back obliquely truncated on 

 each side of the carina. 



This shell differs from A. Texanus in having the back elevated in the middle, and in being 

 without tubercles on the back, in having only two series of nodes on the sides, or with a middle 

 series of rudimentary or obsolete tubercles ; also the serratures of the septal lobes are much 

 wider than in A. Texanus. 



TERTIARY FOSSILS. 



OSTREA, Lin. 



OSTREA VESPEKTINA. 



Plate XVII, Fia. 1, or-d. 

 Ostrea vespertina, Con. Jour. Acad. Nat. Sci., vol. II, (new series) p. 300. 



Ovate-subfalcate ; lower valve plaited or ribbed ; hinge long and wide, sharp and somewhat 

 pointed ; ligament cavity wide, profound, minutely wrinkled ; margins abrupt ; cavity not very 

 deep ; muscular impressions large, impressed ; upper valve flat, irregular ; pallial impression 

 crenulated. 



Resembles 0. subfalcaia, Con. of the Virginia Miocene. 



Localities. — Carriso creek, and near San Diego, California. (Miocene.) 



OSTEEA VELENIANA. 



Plate XVII, Fig. 2, a, b. 



Ovate, flattened, entire, with rugose lines of growth ; cardinal area very broad : ligament pit 

 shallow ; muscular impression very large in proportion to the size of the shell, transverse ; no 

 crenulations visible about the margin. 



This is probably a Miocene shell. 



Locality. — Rancho Heleila, below Salado. 



OSTREA CONTRAOTA. 



Plate XVIII, a, h, c, d. 

 Ostrea contracta, Proc. Acad. Nat. Sci., vol. VII, p. 269. 

 Subfalcate, elongate, thick ; exterior of lower valve very irregular, and varying from ventricose 



