NATURAL SCIENCES OF PHILADELPHIA. 23 



versely subreniform, or a little oval, with a somewhat sinuous inner margin. 

 Surface ornamented by numerous straight costae, which are small and nearly 

 regular on the inner volutions, but become more irregular and larger on the 

 side^ of the body whorl, where they support around each dorso-lateral region, 

 a row of prominent nodes so disposed as to alternate on opposite aides of the 

 shell. 



On the dorsum the costs are of uniform size, with the exception of their 

 regular enlargement with the whorls. The nodes are directed out at right 

 angles to the plane of the shell, and, like the costEe, become again smaller and 

 more closely arranged towards the aperture. Some of the costae bifurcate at 

 the nodes on the body whorl, but their number is also increased by the inter- 

 calation of others between. Where they bifurcate at any of the nodes on one 

 side, the two divisions crossing over the dorsum from the point of bifurcation, 

 never both intersect a node on the opposite side, but, in most cases, one of 

 them, and sometimes both, terminate between two of the nodes on the other 

 side. In crossing over the dorsum, near the aperture, they all curve a little 

 forward, but on other parts of the shell they pass nearly or quite straight 

 across. 



Tne septate portion of the only specimen of this species in the collection 

 being highly crystalline, the sutures of its septa cannot be very clearly traced 

 out. We can see, however, that the dorsal lobe is a little longer than wide. It 

 has a rather narrow body, and is provided with three branches on each side, 

 the upper pair of which are small and nearly simple, while the next pair are 

 longer and bifid, and the terminal pair, which are a little larger than the second, 

 are each ornamented by three small, pointed branches or digitations on the 

 outer side. The superior lateral lobe is somewhat irregularly tripartite, the 

 lateral divisions being bifid and sharply digitate, while the terminal, which i3 

 longer than the others and not exactly central, has about five pointed digita- 

 tions, or sharp, nearly or quite simple branchlets. The lateral saddle is deeply 

 divided at the extremity into two nearly equal branches. The inferior lateral 

 saddle is not more than about one-third as large as the superior, nearly as long 

 as wide and regularly tripartite, while the others have about four digitations 

 each, and show a slight disposition to bifurcate. 



Length, 2-10 inches; height, 1-76 inch; greatest breadth measuring to the 

 extremities of the nodes on opposite sides, 1-25 inches ; do. between the nodes, 

 1 inch. 



This species is related to S. hippocrepis of Dekay, sp. (= Ammonites hippo- 

 crepis, Dekay, An. N. Y. Lyceum, vol. ii. pi. v. fig. 5,) but differs in having its 

 body whorl less extended away from the coil of inner volutions, and in being 

 higher in proportion to its length. Its nodes are also larger and much more 

 prominent; but the most marked difference between these two forms is in their 

 septa, the dorsal lobe of that under consideration being proportionally much 

 narrower and provided with three instead of two branches on each side; while 

 its lateral lobes are distinctly tripartite instead of bifid. 



It is also allied to S. Texanus, Roemer, (Kreid. von Tex., tab. 1, fig. 4.) 

 though its septa differ as widely from those of that shell as from S. hippocrepis. 



Its smaller size, less ventricose form, narrower whorls, and distinct nodes, 

 will at once distinguish it from the last described species, with which it was 

 found associated. Its septa also differ in the tripartite character of its lateral 

 lobes, which is an unusual feature in this genus. 



Locality and position. Same as last. 



Genus AMMONITES, Bruguiere. 

 Ammonites Mullananus. 

 Shell compressed-subglobose; rounded on the dorsum. Umbilicus small, 

 deep and acutely conical, between one-third and one-half as wide as the 



1862.] 



