12.2 



INFERIOR OOLITE AMMONITES. 



RESUME OF THE PRECEDING GENERA. 



I have two things to do in this resume, first to notice the suture-lines, &c, 

 figured upon Plate A, so far as they relate to the species already described ; and 

 next to put forward certain conclusions which a consideration of them, and of the 

 other characters of the species, have induced me to form concerning these 

 Ammonites. 



In the first matter I will notice that in Plate A the suture-lines of various 

 species of Ludwigia 1 are exhibited in figs. 1 — 7 ; and they evidently show the same 

 general characters throughout. These may be briefly recapitulated as — accessory 

 lobe in siphonal saddle slightly developed, inferior lateral lobe very much smaller 

 than the superior lateral, auxiliary lobes feebly developed and few in number. 

 The suture-line of a typical Ludwigia Murchisonce is given in fig. 1, that of 

 Ludwigia Murchisonce var. obtusa fig. 2, of a more adult specimen fig. 3, and that 

 of Lud. Murchisonce var. Baylii fig. 4. Eig. 3 is noticeable for its very short 

 siphonal lobe ; fig. 2 seems to have only two auxiliary lobes ; but otherwise their 

 general characters are practically the same. Fig. 5 represents the suture-line of 

 Ludwigia Lucyi, which differs only in carrying the inner portion rather higher ; 

 but this may not be a persistent feature. Fig. 6 shows the lobe-line of Lud. cornu, 

 and indicates the distance at which the lobes are placed one from the other. This 

 latisept character is a special feature in Ludwigia, which the less developed forms 

 (Lud. obtusa) show in an even more pronounced manner. Fig. 7 gives the suture- 

 line of Lud. rudis, and it is placed just above that of Lioc. apertum for 

 comparison. The greater difference in size of the two lateral lobes in the former 

 compared to the latter, and the fewer number of less prominent auxiliary lobes, 

 may be noticed. 



The suture-lines of the genus Lioceras 2 are illustrated by figs. 10 — 17. They 

 show a more developed accessory lobe in the siphonal saddle, a larger inferior 

 lateral lobe, especially in comparison with the superior lateral, and a greater 

 number of well-developed auxiliary lobes. The ends of the siphonal lobes are less 

 divergent than in Ludwigia. Most of the chief lateral lobes decrease in gradually 

 descending order, though sometimes the auxiliaries are a little irregular in this 

 respect. The whole aspect of the lobes shows a more florid style of ornamentation 

 than is met with in Ludwigia. Fig. 10 is the lobe-line of a young specimen of 



1 Pages 16 — 20, 101 — 108. The sutures of this genus exhibited in Plate II, fig. 5, are not quite 

 trustworthy ; the superior lateral lobe is too long, and the inner portion is not finished off. 



2 Pages 21—80. 



