124 INFERIOR OOLITE AMMONITES. 



We now come to a very different style of suture, and to find any approach to it 

 at all we must go back to fig. 2 (Ludwigia obtusa) ; but even this is in many ways 

 different. Two figures, 28, 29, illustrate the suture-line of two forms of Hildoceras 1 

 bifrons, the latter taken from a thick evolute specimen from the Upper-Lias Clay, 

 Somerset, the former from a compressed involute example from the Cotteswold 

 Sands in Gloucestershire. 2 Both agree in possessing a narrow ventral lobe closely 

 embracing the siphon, a very wide siphonal saddle with an undeveloped accessory 

 lobe, and a broad- stemmed, rather short, superior lateral lobe; but the latter (fig. 

 29) has its inner lobes elevated as if cramped for room, the former (fig. 28) has the 

 inner lobes in line and stretched as if they could not properly fill up the space ; for 

 this purpose, too, it has had to produce some denticulations. Practically only one 

 auxiliary lobe is present in either. 



Some lobe-lines of the genus Poecilomorphus 5 are presented in figs. 31, 32, 33, 

 all enlarged about six times the natural size. Fig. 31 is a copy from d'Orbigny 

 ' Ceph. Jurass.,' plate 121 (Am. cycloides). Fig. 32 I have taken from a medium 

 specimen in my collection. There is a certain amount of difference between the 

 two. The siphonal lobe of fig. 31 is narrower, while the accessory lobe therein is 

 more developed than in fig. 32 ; the inner part of fig. 31, including the superior 

 lateral saddle, inferior lateral lobe and saddle is broader than in fig. 32 (p. 121). 

 Fig. 33 shows the suture-line of Poecil. macer, which is apparently intermediate 

 between the last two. It exhibits the accessory lobe in the siphonal saddle like 

 fig. 31 ; but this siphonal saddle is broader, while the superior lateral saddle is 

 narrower, than in that figure. The inferior lateral lobe is also narrower, and 

 except for the accessory lobe in the siphonal saddle the suture agrees more with fig. 

 32 than with fig. 31 (d'Orbigny's). 



The remaining suture-lines must be reserved for discussion until the species to 

 which they belong have been figured and described. It only remains for me to 

 notice the radial lines. These I have taken from the inner edge to the middle of 

 the carina, in contrast with a straight line drawn from the centre of the umbilicus 

 to the tip of the rib upon the carina. The following types of ribbing may be 

 observed : 



Fig. 8. Recurved bifurcate, taken from the specimen of Ludwigia Murchisonce 

 figured on Plate III, fig. 1. V= middle of ventral lobe. 



Fig. 18. Sigmoidal, taken from a typical Lioceras concavum ; I' ■=. middle of 

 superior lateral lobe, I" = of inferior lateral lobe. 



Fig. 19. V-shaped, changing toiuards sigmoidal, taken from a specimen of 

 Lioceras concavum var. 



1 Pages 111—114. 



3 In the involute form the whorl overlaps to the lateral sulcus ; in the other it leaves as much 

 exposed outside the sulcus as there is inside. 3 Pages 115 — 121. 



