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Show 369 AMMONITES COMPLEXUS?, var. SucrAENSis. Plate 5, figs. 2 and 2 a, b, c. Ammonites complexus, Hall and Meek ( 1856), Mem. Am. Acad. Arts and Sci. Boston, T, ( new series), 394, pi. 1, fig. 1, a-/. ^ « i9ntfc » o » ijffecuJ, var. Sudaenth, Meek ( 1861), Proceed. Aoad. Nat. Sci. Philad., xiii, 317. AmmoniUi Sudaensis, Gabb ( 1869), California Geol. Report, i, 133, pi. 21, figs. 11 and 11 a, b Shell attaining a moderate size, discoid, ronaded oa the periphery;. aasbilioas shaHow- erateriform, about half as broad as ttas outer volution from the dorsal to the ventral side, and showing nearly one- third of each inner tarn; volutions apparently about five or six, increasing rather gradually in size, last one very slightly compressed on the sides, and rounding to the periphery and umbilicus, all deeply embracing. SOT face ornamented by transverse costo, which, in the very young shell, appear to be merely little elongated nodes near the umMliaus, bnt in a more advanced stage of growth cross the sides, and pass straight over the periphery as narrow low ribs, separated by wider flattened depressions, while on the outer turn of large shells they seem to be nearly obsolete ; between each two of those that extend inward to the umbilical side, there is usually one, or sometimes two, that become obsolete before reaching the inner margin, while those that extend entirely across swell a little near the umbilicus so as to show a tendency to develop obscure, elongated nodes. Septa profoundly divided into slender, variously- branched, and digitate lobes and sinuses. Siphonal lobe nearly as large as the first lateral lobe, and ornamented on each side by four branehes, which increase in size, and become more subdivided toward its extremity, the two terminal divisions being considerably larger than the others, and each divided into four or five unequal digitate, spreading branchlets. First lateral sinus as large as the siphonal lobe, about one- third longer than wide, slender and flexuous near the base, and very deeply divided above into two subequal slender branches, each of which is subdivided so as to form three or four unequal, more or less bifurcating, and deeply sinuous branchlets. First lateral lobe one- third longer than wide, and ornamented at the extremity by three great spreading, nearly equal, branches, each of which is subdivided into three or four principal branchlets, with numerous smaller digitate subdivisions. Second lateral sinus as long as the first, but narrower, and very similarly divided. Second lateral lobe nearly two- thirds as large as the first, and closely resembling it in its branches and subdivisions. Third lateral lobe about half as large as the second, with somewhat similar but less deeply-divided branches. There are three or four other much smaller lobes between the third lateral lobe and the umbilicus, which are very oblique, and each more or less distinctly trifid and digitate at the extremity. I have endeavored to give a full and detailed description of this shell, because, after a very- careful comparison, I am left in doubt whether it should be regarded as a variety of A. complexus ( Hall and Meek) or as a distinct species. It certainly is a much more compressed shell, the volutions of A. complexus being nearly twice as wide transversely as from the dorsal to the ventral side, while these two diameters of the whorls in the form before me are nearly equal. Differences of this kind, however, are not generally reliable as a means of distinguishing species in this group; though the few specimens of A. complexus yet brought |
