361^ 

 Ammonites cjomplexus!, var. SuorAENwis. 



Plate 5, fig3. 2 aad 2 a,J>, c. 



Ammonites CO nqylex us, Il-dll and Meek (1856), Mem. Am. *Acad. Arts and Sci. Bo.stou,'T, 



(new series), 394, pi. 1, fig. 1, «-/. 

 Ammonites conwlexas, var. Sudaensis, Meek (1861), Proceed. Acad. Nat. Sci. Piiilad., xiii, 



317. 

 Ammonites Sudaensis, Gabb (1869), Califoruia Geol. Report, i, 133, pi. 21, figs. 11 and 11 ffl, & 



Shell attaining a moderate size, discoid, rounded on the periphery ; 

 umbilicas shallow-crateriforoi, about half as broad as the outer volution 

 from the dorsal to the ventral side, and showing nearly one-third of each 

 inner turn; 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. Sur- 

 face ornamented by transverse costai, which, in the very young shell, 

 appear to be merely little elongated nodes near the umbilicus, but in a 

 more advanced stage of growth cross the sides, and pass straight over 

 the i>eriphery as narrow low ribs, separated by wider flattened depres- 

 sions, while on the outer turn of large shells they seem to be nearly ob- 

 solete ; between each two of those that extend inward to the umbUical 

 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 digi- 

 tate lobes and sinuses. Siphouai lobe nearly as large as the first lat- 

 eral lobe, and ornamented on each side by four branches, which in- 

 crease 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 branclilets. 

 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 lat- 

 eral 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 comi)arison, 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. Difl:erences 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 



