MEXICAN BOUNDARY LINE. 159 



A large and beautiful species, witli the shell converted into carhonate of lime. Named in 

 honor of its discoverer, Arthur Schott, esq. 



NODOSAPJA, Lam. 



NODOSARIA TEXANA. 



Plate XIV, Figure 4, a, b, c. 



Straight or slightly curved, subulate, nodes transversely oblong or depressed, ventricose, 

 numerous. 



Very abimdant in the form of casts. The outline of the shell appears to have been nearly or 

 quite straight below, and somewhat curved towards the apex. 



Locality — Between El Paso and Frontera. 



AMMONITES, Lam. 



AMMONITES PLEUEISEPTA. 



Plate XV, Fig. I, a,h, c. 



Discoid, much compressed, lentiform ; back acute ; volutions with obscure, distant, transverse 

 ribs or undulations, and two series of nodules — one central and distinct, the other obsolete — 

 elongated transversely and near the margin or back; transverse section of the whorls lanceolate; 

 umbilicus very small ; series of sutures of the septa crowded, gradually separating as they 

 approach the inmost whorl ; septal lobes short, suddenly expanded, crenulate, rounded ; saddle 

 bilobed, the lobes obtusely rounded, the third lobe from the dorsal the largest of the series. 



This species approximates A. jiedernalis, Koemer, who supposes it to be identical with the 

 foreign species of that name described by Von Buch. It differs from Roemer's shell in having 

 tubercles, in being less compressed, or forming a less acute angle with the back ; in having a 

 smaller umbilicus, and transverse undulations, and also in more crowded and very differently 

 shaped septa. It attains a much larger size tnan the specimen figured. 



Locality. — Jacun, 3 miles below Laredo. 



AMMONITES GENICULATUS. 



Plate XV, Fig. 2, a, h. 



Discoid, sides flattened and gradually sloping towards the back, which is abrupt, slightly 

 rounded, and with a thick, prominent carina on the middle ; ribs numerous, slightly curved 

 until they approach the back, when they suddenly bend and become very oblique and more 

 prominent, obsolete on the back ; inner sides of the volutions abrupt. 



Allied to A. flaccidicosta, Roemer, but maybe distinguished by^the dorsal carina and broader 

 arms of the septal lobes, and flattened instead of rounded volutions ; and also by the different 

 form and inclination of the ribs. 



Locality. — Bed of Rio San Pedro, and Leon Springs. 



AMMONITES TEXANUS. 



Plate XVI, Fig. I, a, d. 

 Ammonitse Texanus, Eoemer ; Kreid. von Texas, pi. VI, fig. 2, a, h. 

 Large, somewhat discoidal, involute ; volutions subquadrangular, gradually increasing in 



