LUDWIGIA MURCHTSONjE. 19 



three forms, that of L. obiusa being the simplest. On Plate II, fig. 5, is a 

 drawing of the suture line of Sowerby's original specimen of this species, made 

 expressly for comparison with that of Lioceras. It will be noticed that the lobes 

 are somewhat long and narrow and the saddles rather deep. A small accessory 

 lobe divides the siphonal saddle, while the superior lateral may be said to be 

 quite undivided. The inferior lateral lobe is very much smaller than the superior; 

 and it should be observed that the sutures are apart from each other, hardly 

 anywhere overlapping. Though this perhaps can scarcely be treated as a 

 generic difference, yet it is more the rule in Ludwigia and the exception in 

 Lioceras. 



This species occurs in the zone of the same name. Good typical examples of 

 it are uncommon in the South of England, and the variety L. Baylii is the rarest 

 of the three forms. They are generally met with in a very poor state of preserva- 

 tion, and in fact all the good specimens with which I am at present acquainted 

 came from Bradford Abbas, where it occurs in a bed of light brown, some- 

 what soft stone called the Paving Bed, from the fact that it can be taken up in 

 large layers or slabs and hardens on exposure, when it can be used for flooring. 

 The zone of Murchisonae is met with in many places, viz. Sherborne, Bradford 

 Abbas, Halfway House (Compton), Beaminster, Burton Bradstock, &c, in 

 Dorset ; Haselbury, Misterton, Stoford, Corton Downs, &c, in Somerset, from most 

 of which places specimens of either the typical or varietal forms have been 

 obtained. Dr. Wright quotes the species from Cleeve, Frocester, and Leck- 

 hampton Hills in Gloucestershire. Sowerby's type specimen came from Scotland. 



Plate I represents a fine typical example of this species in very perfect 

 preservation. Plate II, figs. 1, 2, represent the original specimen named and 

 figured by Sowerby and reproduced here (side and front views instead of three 

 quarters front) for reference and comparison. Fig. 5 represents the suture line 

 of this specimen, and is the typical suture line of the genus Ludwigia. 

 Figs. 3, 4, represent a young shell of this species showing its open umbilicus in 

 youth. On Plate III, figs. 1 and 2, is represented a medium-aged specimen in 

 very good preservation, and of the size usually found. It is figured to show 

 the transition from ribs to lines of growth, and also the bifurcating, reflexed ribs 

 better than the other specimens. Fig. 3 is given to show the termination of the 

 body-chamber, and is the only example at present under my notice. The lateral 

 lappet of the termination is not complete and some other parts of the specimen 

 are somewhat poorly preserved. Figs. 4, 5, show the characters of the variety 

 L. obtusa with its coarse, knotted ribs, and its quadrangular section. The 

 keel of this specimen is rather badly preserved and, perhaps, is more prominent. 

 Figs. 6, 7, show the variety L. Baylii and its different aspect from the others. I 

 have a larger specimen showing the characteristics of this variety (which becomes 



