218 INFERIOR OOLITE AMMONITES. 



course, on the outside of the whorl ; and, similarly, on a small specimen from 

 Milhau I can count seven to the top of the inner margin. 



The suture-line of this species is, as I have said, extremely hard to follow ; and 

 this is due not only to the extraordinary complexity of the septa of a series of 

 chambers very closely crowded together, but also because the suture-line may not 

 be absolutely separated from its predecessor. In fact, in many places — and I 

 have observed the same in the complex sutures of other species — the lobes are 

 sometimes distinctly joined to the saddles of the preceding suture at one or two 

 points ; and the consequence is that in tracing a suture-line under such circum- 

 stances one is apt to branch off, at the point of junction, on to the wrong suture- 

 line. 



I could wish that I had more material of this species, so as to give its history 

 from the earliest period. Failing that, the following notes upon the suture-line 

 may be of service. When the side of the whorl is 3^ lines broad the siphonal lobe 

 is fairly simple. It is not, however, so simple as in adult Haiyoceras, but shows 

 a certain addition in the way of follicles ; and also it is more divergent and not so 

 dependent. (Fig. 4 in PL XXXVII shows the terminal branch of the siphonal 

 lobe when the whorl is 3^ lines broad ; but of course the drawing is much 

 enlarged.) At this time the accessory lobe in the siphonal saddle is large and 

 well developed, and its lowest point hangs level with point d, fig. 4 ; the superior 

 lateral lobe is large, and is just longer than the siphonal ; the inferior lateral 

 lobe is little larger than the accessory lobe ; and there are four fairly conspicuous 

 auxihary lobes, and a fifth rudimentary. 



At this age the only points in which the suture-line differs from that of 

 Harpoceras are the slightly more developed siphonal lobe, and the more con- 

 spicuous auxiliary lobes ; while the large accessory lobe is so characteristic of 

 Haiyoccras. 



Although the whole suture-line gradually increases in complexity as the shell 

 grows, yet there is a very noticeable, in fact much quicker, development in the 

 branches of the siphonal lobe. When the whorl is 5|- lines broad — that is 

 to say, just at the ninth suture onwards — the terminal branch of the siphonal 

 lobe shows the form represented (enlarged) in fig. 5. It will be noticed 

 that the points marked a — e have all very much developed from the same 

 points in fig. 4 ; and that, on account of a rather greater growth in c — e, the 

 terminal branch stands out still more conspicuously from the keel-line than it 

 did before (fig. 4). Not only have the various points a — e increased in size, 

 but they also show several additional minor points which indicate the manner 

 in which further development of the lobe in the matter of complexity could be 

 brought about. 



The remainder of this suture is more complex than the one formerly described ; 



