8. S. Biichman — On Jurassic Ammonites. 397 



area when the test is present or absent ; but the keel of Am. falcifer 

 is separated from the mould by an inner laj'er of shell ; and the two 

 sides of the keel and this layer form a triangle inclosing a hollow 

 space, which has become filled with mud. Where, therefore, the test 

 is absent, the mould of Am. falcifer becomes rounded on the ventral 

 area. This kind of keel is well shown by Dr. Haug, Beitrage 

 Monogr. Harpoceras, plate xi. fig. 1, for Am. variabilis ; and it is to 

 be seen in the genera Hammatoceras, Sonninia, etc. ; but this structure 

 of the keel is not shown in the genera Hildoceras, Luchviyia, Lioceras, 

 etc. It therefore seems right to separate Am. falcifer generically, 

 and since Dr. Haug has proposed to restrict Waagen's genus Harpo- 

 ceras to a small group of which Am. falcifer is the type, we desire to 

 follow such a good suggestion. 



G-enus Haupooekas, Waagen, emend. Haug. 



Ribs sickle-shaped, much produced on ventral area. Keel distinct 

 and hollow, separable from the mould ; ventral area of mould 

 rounded when keel absent, no furrows on either sides of the keel, 

 inner margin square ; large accessory lobe in siphonal saddle ; large 

 and much branched superior lateral lobe ; inferior lateral and 

 auxiliaries retracted.' 



Haepoceras falciferum (Sowerby). 



1822. Ammonites falcifer, Sowerby, Min. Conch, t. 2o4, fig. 2. 



1846. serpentinns, D'Orbigny (nou Eeinecke), Pal. fr. t. 55. 



1878. Lioceras serpentinum, Bayle, Explic. carte geol. iv. t. 87, figs. 2-3. 



1882. Harpoceras serpentinum, Wright, Lias Am. t. 58. 



The above list of references will at once show how this Ammonite 

 has been misunderstood. D'Orbigny, Wright, and other authors 

 have extinguished Sowerby's names of Strangewaysi and falcifer, 

 considering them to be the same and also equivalent to Eeinecke's 

 serpentinus. In this they were perhaps right as far as Am. Strange- 

 ivaysi is concerned, which is very near to Eeinecke's Am. serpen- 

 tinus ; but Sowerby was certainly correct when, having the two 

 specimens in front of him, and putting them for comparison on the 

 same plate, he made them two different species ; and it is singular 

 that D'Orbigny, Wright, etc., should have figured as Eeinecke's 

 serpentinus what is really Am. falcifer, for a comparison of the inner 

 edges of the whorls should have shown this to be a mistake. 

 Sowerby distinctly says of Am. Strangeioaysi, "inner edges of the 

 whorls obliquely flattened," and of Am. falcifer that it differs from 

 Am. Strangeioaysi by " wanting the flat surface of the inner margin 

 of the whorl," and Eeinecke distinctly shows the section of his 

 serpentinus (fig. 75) with the inner margin obliquely flattened. Again, 

 the coiling is very different. In Eeinecke's serpentinus it is regular 

 throughout; in Wright's figure it is irregular, that is, the inclusion 

 becomes less with every whorl. Eeinecke's serpentinus, which is 



1 Compare genus Eildoceras. Mould showing shape of keel ; ventral area flattened 

 or furrowed ; inner margin subconcave, sloping. Very broad siphonal saddle, small 

 accessory lobe, superior lateral lobe little branched, inferior lateral and auxiliaries 

 produced. 



