S. S. Biichnan — On Jurassic Ammonites. 399 



name of Am. elegans, Young, ought in reality to be cancelled ; but 

 we know from Young that it has a concave inner margin, and 

 Wright has given a very good figure of a shell of this kind, which 

 agrees with Young's description, and as this shell of Wright's would 

 belong to a different genus, and possesses no other name, perhaps it 

 is as well to retain this one. Also, since it belongs to the genus 

 Lioceras, it would be correctly stated as Lioceras elegans (Young, 

 or Wright), and would be well distinguished from Earpoceras 

 elegans (Sowerby). 



There is one point about this latter species, namely, that Sowerby 

 states that the siphuncle is within the keel. As Harpoceras in its 

 restricted definition is distinctly not so, we think he may have mis- 

 taken the hollowness for the siphuncle, as he did in his figure of Am. 

 Sowerhiji, pi. 213. 



Hakpocekas exaratum, Wright. 



1822. Ammo7iites exaratits, Young and Bird, Geol. Surv. Torks. p. 266. 

 1882. Harpoceras exaratimi, "Wright, Lias Am. Pal. Soc. pi. 62, fig. 1. 



As Young does not give any figure of his species, we cannot say 

 what it may be, and therefore accept Wright's figure as the tyjje of 

 the species. It seems, judging from the figure, to belong to the 

 genus Harpoceras. It is certainly not, as Wright has mentioned 

 in his synonyms, Am. complanatus of D'Orbigny, which has a very 

 different sectional view and smaller centre. This species has the same 

 sized umbilicus as Harp, elegans (Sow.), but differs in the sectional 

 view, the sides being less sloped towards the venti'al area. If there 

 are no other differences, I should be inclined to regard this shell as 

 merely a variety of Sowerby's H. elegans. 



Harpoceras subplanatum (Oppel). 



1844. Ammonites complanatus, D'Orb., Terr. Jnr. p. 353, pi. 114, figs. 1-2. 

 1856. subplanatus, Oppel, Juraf. p. 244. 



Dr. Wright has given Am. complanatus, D'Orb., as a synonym of 

 Harp, exaratum ; but I think that a comparison of the centres and 

 the section of D'Orbigny's and Wright's figures will show this to be 

 a mistake, and Dr. Hang (p. 619) has wisely separated the two 

 species. Dr. Haug has included both of these species in the group 

 oi Am. falcifer, and also ^m. discoides ; but I am inclined to think 

 that Am. discoides should be separated. It has a likeness in regard 

 to its ribbing, but it has in reality no keel, only the ventral area 

 sharpened, and, judging from the suture-line, I consider that it does 

 not belong to Harpoceras at all, but should be classed in proximity 

 with Oppelia. Harp, subplanatum occurs in England ; by the kind- 

 ness of Mr. B. Thompson, F.G.S., I have been able to examine a 

 specimen from Northamptonshire. 



We have, therefore, in the genus Harpoceras, Harp, falciferum, 

 Sow., Harp, elegans, Sow., Harp, exaratum (Young), Wright, and 

 Harp, suhplanatum, Oppel ; whilst Am. serpentinus, Reinecke, 

 perhaps belongs to the genus Hildoceras, and as the -species was not 



