LIOCERAS BRADFORDENSE. 23 



this species answers in general to the description given of that of the genus. It 

 differs in no important points. The accessory lobe dividing the siphonal saddle 

 is not so large as in Lioc. opalinum. 



This species occupies a most extraordinary position. As its age varies it so 

 nearly approaches in shape either to Lioceras concavum or else to Ludwigia Mur- 

 chisonce, that until we had the evidence of the suture line it was a constant source 

 of perplexity to decide its true position. Ludwigia Murchisonce is also such a 

 variable form that it seemed quite possible to include this species, occurring as 

 it does in the same bed, as one of its varieties. This is the view that I took 

 in 1881, in the reference quoted above, and is also the view taken by Prof. 

 Quenstedt in his ' Jura,' plate xlvi. It has no doubt been figured in other places 

 under the name of Am. Murchisonce ; for so closely does our species some- 

 times simulate the varieties of the latter that unless we had the additional 

 evidence of the suture line we should often be unable to identify figures. 

 Again, this species is not at all easy to separate from specimens of Lioceras 

 concavum in middle age. There can, however, be no difficulty with the adult 

 forms, because the umbilicus of Li. Lradfordense is then large and open, while that 

 of Li. concavum keeps to its small hollow form. The best distinction between 

 middle-aged Li. lradfordense and Li. concavum is that in the umbilicus of the 

 former a small portion of each of the inner whorls is exposed, forming small steps 

 and showing the ribs, while in Li. concavum this is not the case. Did we, however, 

 not possess the large adult forms of this species, it would seem scarcely sufficient 

 to make a distinction between it and Li. concavum. The most peculiar character 

 about this species is its approach to the form of Ludwigia Murchisonce when it 

 is rather more than half grown, and to Li. concavum when younger. In fact, it 

 possesses the shape of Ludwigia except from young to middle age, while it has 

 the suture line of Lioceras. It should be noticed that Quenstedt's figure, referred 

 to as a synonym of this species, gives the suture line very clearly, figures 4 and 5, 

 plate xlvi (' Der Jura '), illustrating the difference in the suture line of Ludwigia 

 and Lioceras. We can note that in Ludwigia the suture lines are far removed 

 from one another, are rather simpler, and possess only a very rudimentary accessory 

 lobe to divide the siphonal saddle, whereas we see the suture lines of Lioceras 

 more or less overlapping, much closer together, and possessing a well-developed 

 accessory lobe in the middle of the siphonal saddle. 



Lioceras lradfordense is not a common shell, and on account of the nature of 

 the beds it is seldom well preserved. It belongs to the Murchisonse-zone, and in 

 Dorset it has been obtained from Bradford Abbas and other quarries near. From 

 near Beaminster the larger adult examples mostly come, and it is here more 

 frequent. From East Coker in Somerset I have seen very large examples, but 

 they are generally fractured in all directions. 



