228 Mr. II. Seeley on Ammonites 



The back is ,1 little inflated. The keel is round, wide, moderately 

 elevated, with the smooth spaees on each side slightly depressed. 



The mouth is a little wider than high. 



Septa very like those of the southern forms of A. rostratus (to 

 which the form is nearly related), but with the lobes deeper, and 

 with finer digitations. The dorsal, lobe is as long as the back 

 is wide, extends in width to the line where the ribs arise, has 

 two rather narrow branches on each side, and terminates in two 

 acute branches conspicuous in having no digitations on the 

 inner side. The lateral lobe is in the middle of the side, not 

 quite so long as that of the back, with two branches on each 

 side, and terminating in three, of which the middle one is much 

 the largest. At a diameter of If inch the distance between two 

 septa where they cross the keel is fths of an inch. In examples 

 of the southern form of A. rostratus, at a diameter of 2-j? inches 

 the interseptal space on the keel is only half an inch. 



Much as it differs, I incline to regard this as a constituent 

 variety of A. rostratus, with near affinities to A. inflatus. 



Ammonites Timotheanus, Pictet, Gres Vert, pi. 3. figs. 1 & 2. 



Few quadrate whorls, enlarging rather rapidly, two-thirds 

 embracing, gibbous ; with a flat back, flattened sides, and flat 

 ventrum. The sides, very slightly inflated, round into the um- 

 bilicus and into the back, slightly converging, so that the back 

 is narrower than the base. The mouth is nearly a fourth wider 

 than high. The umbilicus is not shallow, and is half as high as 

 the mouth is wide. The cast is perfectly smooth, and only 

 marked with the elegant foliations of complex septa. 



The siphuncle is unusually wide, being of the width of the 

 dorsal lobe. The septa are almost exactly the same as in A. 

 latidorsatus (Mich.). The dorsal lobe is relatively a little deeper 

 by the terminal branches being separated for only half as far; 

 these and the preceding branch on each side are bifid. The 

 superior lateral lobe is deeply cleft, making the two bifid ter- 

 minal branches large. The superior lateral saddle is not deeply 

 cleft. 



I have seen but two specimens of this form, both collected by 

 Mr. Carter. So far as figures and descriptions enable me to 

 judge, it might be classed as a variety of A. latidorsatus, differing 

 chiefly in the flatness of the back, and perhaps in the rate of 

 enlargement; but it appears, from Miehelin's figure, that the 

 young states are sufficiently unlike to justify a distinction. This 

 form always had a flat back and trapezoidal mouth, &c, while 

 the other has a round back and lune-shaped mouth. It exactly 

 corresponds with the Ammonite figured by Prof. Pictet in the 

 'Gres Vert' (pi. 2. fig. 0) as A. Timotheanus ; but it does not 



