LIOCERAS OPALINUM. 39 



elegans. Specimens that I have from Yorkshire show these ribs very well, and 

 they are quite different from the striae of Lioc. opalinum. Vacek's Harpoceras 

 elegans, which is here quoted as a synonym, does not seem to show this character, 

 and, judging from the side view, it has the ventral area almost uncarinated like 

 Lioc. opalinum. In my list of synonyms Dumortier's figures of Am. concavus are 

 also quoted ; but they are not the Am. concavus of Sowerby, as a comparison with 

 my figure of Sowerby's original specimen will show (PI. II, figs. 6, 7). They are 

 generally supposed to be Am. elegans, but they do not show the ribbing of Lioc. 

 elegans (Young), nor are they Harpoceras elegans (Sowerby). The shells seem to 

 be two different forms, either closely allied to Lioc. opalinum or else intermediate 

 between it and Lioc. elegans ; in fact, they can scarcely be said to agree exactly 

 with the types of either species, although the fine ribbing and the sectional view 

 of fig. 3 with little carina approach more to Lioc. opalinum than to Lioc. 

 elegans. 



Besides the form of Lioc. opalinum which since it agrees with Reinecke's figure 

 I consider typical (Plate XIII, figs. 4, 5, and adult, figs. 1, 2), I have met with 

 other forms showing a slight amount of difference usually traceable from youth to 

 adolescence in any considerable series of specimens. The most distinct is perhaps 

 the thin form, which is rather the commoner, and differs from the type by its 

 shallow, more open umbilicus, with very sloping walls, and in being thinner (Plate 

 XIII, figs. 7, 8, 9, 10). Then there is the form figured in Dr. Wright's Mono- 

 graph (Plate LXXX, figs. 5, 6), which is somewhat thicker than the typical form. 

 Besides these we have certain forms, with false ribs on the inner area, connecting 

 us with the variety comptum, which I will consider under that heading. 



From this species I would expressly exclude certain specimens which are rather 

 frequently met with in the Cephalopoda-bed of the Cotteswolds, and seem to very 

 closely resemble the figure given by Lepsius previously quoted. Indeed I feel 

 certain that, nothwithstanding their similarity in many respects, especially to the 

 open-centred form of Lioc. opalinum, yet since they possess a less complex suture- 

 line with practically only one small auxiliary lobe, they really belong not only to 

 another species but to another genus. When closely compared with Lioc. opalinum 

 they are seen to have straighter ribs on the lateral area (ribs and not striae as in 

 the case of Lioc. opalinum), and also to possess a more prominent and trenchant 

 carina. The width of the umbilicus, with its rather upright walls, is at all ages 

 considerably in excess of that shown in the open Lioc. opalinum. I cannot help 

 thinking that it is this species having a close affinity to Grammoceras Moorei 

 (Lycett), that has partly given rise to the opinion of that species being only a 

 variety of Lioc. opalinum. 



The absence almost of even a sub-carina in Lioc. opalinum, except in the young 

 state, and the rounded character of the ventral area (all trace of keel being lost), 



