LIOCERAS DECIP1ENS. 31 



of the umbilicus at the body-chamber. From Lioc. ambiguum its front view, more 

 parallel sides, and smaller umbilicus, will distinguish it. 1 



The horizon of this species is very easily determined because in the matrix 

 of the body-chamber of the figured specimen are embedded some examples of 

 Iihynckonella ringens. This would prove it to come from the lower part of the 

 Soiverbyi-zone (Concavum-beds) . Judging from the matrix, the species occurs 

 near Sherborne, Dorset ; but it is certainly scarce, and I do not know of it in any 

 other part of the district. 



Plate XII, fig. 8, represents a good specimen of this species with its test well 

 preserved. The whole of the body-chamber is present and a part of the termination. 

 [The piece of test on the body-chamber has been transferred from the other side 

 of the specimen for the purpose of figuring.] 



Lioceeas decipiens, var. simile, 8. Buchman. Plate XV, figs. 1, 2. 



I have only this one specimen of a very peculiar form, which is so well 

 preserved and has such marked and yet similar characters, that I have thought it 

 well to distinguish it by a varietal name. Mr. Gawan has given a very good figure 

 of it, from which it will be seen that it has a great resemblance to Lioceras 

 decipiens ; but it differs in possessing very small ribs on the outer area at a later 

 age, in having a much smaller umbilicus with deeper walls, and in being consid- 

 erably thicker. We perceive what is probably the commencement of the termination , 

 and the X shows the length of the body-chamber. There is a peculiarity in 

 the structure of the carina, which is broadish, rounded, distinct from the ventral 

 area, and yet not prominent, which, together with the smoothness of the test, at 

 once seem to unite this form to Lioc. decipiens. If we compare the figure of 

 this form with the large figure of Lioceras giganteum, we see much resemblance, 

 and, did we not possess a series of smaller specimens of the latter, we might 

 reasonably consider Lioc. simile to be the young of Lioceras giganteum. The 

 umbilicus of Lioc. simile is fairly well preserved, and allows of examination, 

 but the large specimen of Lioc. giganteum does not possess quite all the umbilicus 

 drawn by the artist. This umbilicus of Lioc. giganteum as thus filled in does not 



1 It was not until this sheet was passing through the press that I was able to obtain and study 

 Quenstedt's work (' Amm. Schwabischen Jura'). Ammonites Murchisonce planatus (pi. lix, figs. 

 16 and 17) has close resemblance to this species and its varieties. It evidently belongs to the genus 

 Lioceras and should not be classed with Murchisonce (Ludwigia) as Quenstedt has done. It differs 

 from Lioc. decipiens and simile in having a larger umhilicus with more whorls, also in having narrower 

 and more quadrate whorls with shorter aperture, so that, though closely allied, it is evidently not the 

 same, but might, perhaps, eventually be conveniently classed as a variety. Lioc. decipiens, simile, and 

 intermedium, with Quenstedt's Am. Murchisonce planatus, seem to form a small, closely-allied scries of 

 smooth Liocerata. 



