384 Systematic Paleontology 



" Septa rather deeply divided into four principal lobes and as many 

 sinuses on each side of the siphonal lobe, which is nearly oblong in form, 

 about twice as long as wide, and bears three slender digitate main 

 branches on each side, the two terminal of which are a little longer than 

 the others; first lateral sinus as long as the siphonal, and a little wider, 

 provided with three nearly equal, slender, deeply incised and digitate ter- 

 minal branches and smaller lateral divisions ; first lateral lobe as long as 

 the siphonal, and nearly of the same breadth at its free end, where it is 

 provided with two unequal branches, the larger of which (that on the 

 inner side) is subdivided into three digitate branchlets, and the smaller 

 into two, while its slender body supports one or two small, partly digitate. 

 diverging lateral branchlets; second lateral sinus shorter than the first, 

 and scarcely more than half as wide, with two nearly equal bifid and ser- 

 rated terminal branches, and several short obtuse, irregularly notched, 

 alternating lateral divisions, the sinuses between which are so deep as to 

 give the body a very narrow, zigzag appearance; second lateral lobe a 

 little more than half as long as and wide as the first, and provided with 

 two bifid and digitate terminal branches and one small, nearly or quite 

 simple, diverging lateral branchlet on each side of its slender body; third 

 lateral sinus shorter than the second, but of nearly the same breadth, 

 with a very slender body and two nearly equal, irregularly trifid sub- 

 divisions ; third lateral lobe rather more than half as long and wide as the 

 second, and very similarly formed ; fourth lateral sinus half as long and 

 wide as the third, with two small, irregularly serrated, terminal branches ; 

 fourth lateral lobe small, and bifid at the end, the two divisions being very 

 short and bi- or tri-dentate. 



"Length of largest example, 6.30 inches; height of same, 5.70 inches; 

 convexity, about 2.70 inches. 



" . . . . The specimens of this species figured by Dr. Owen under the 

 name Ammonites nebrascensis have the deflected part of the outer volu- 

 tion broken away, in which condition they are, of course undistinguishable 

 from the genus Ammonites, as formerly understood in its more compre- 

 hensive signification. 



