162 Rev. J. F. Blake — On Ammonites. 



Geniohyiis fajnmensis, sp. nov. 



Another specimen, consisting of a portion of the mandible con- 

 taining the premolars in a perfect state of preservation, was also 

 collected. This may be taken as indicating the existence of a second 

 species of Geniohyiis, since the teeth, though similar in general form, 

 differ considerably in many details. The chief of these diiferences 

 are that the main cusp is already distinctly divided in pm. 2, and. 

 the hind lobe in all the teeth is much larger and more distinctly 

 selenodont. 



The structure of the teeth is as follows : — Pm. 1 is strongly com- 

 pressed with a very small anterior cusp and a high main cusp, from 

 which three ridges diverge posteriorly, one running down the 

 outer face of the tooth, a second back to the anterior arm of the 

 V-shaped posterior cusp, the third inwards down the inner face 

 of the tooth. The posterior lobe is distinctly selenodont. 



In pin. 2 the anterior cusp is larger, and the ridge running inwards 

 from the main cusp bears a small tubercle at its inner end. The 

 posterior lobe is larger than in pm. 1. Pm. 3 has a larger anterior 

 tubercle, and the cusp on the inner side of the main cusp is now 

 nearly as large as that element and is clearly separated from it. The 

 postei'ior V is still larger. Pm. 4 is similar, except that the small 

 anterior cusp is doubled, the posterior lobe is still larger, and there 

 are traces of a small postero-internal cusp. 

 The dimensions of the premolars are : — 



Length. Breadth. 



pm. 1 ... ... 13 mm. ... 7 mm. 



pm, 2 13 ,, ... 8 ,, 



pm. 3 15 ,, ... 10 ,, 



pm. 4 16 „ ... 12 ,, 



EXPLANATION OF PLATE VI. 



Fig. 1. — Left upper molars and premolars of Arsinoitherium andreivsi, Lankester, 

 ,, 2. — Left lower molars and premolars of the same. 



The two specimens figured belong to one individual, which is the type of the 

 species. About one-fourth nat. size. 

 ,, 3. — Outer face of last upper molar of the left side of Arsinoither'mm zitteli, 

 Beadnell. 



In Figs. 1, 2, and 3: a.c. anterior column of molar; p.c. posterior 

 column of molar ; x, anterior inner cusp ; y, posterior inner cusp. 

 ,', 4. — Upper and side views of part of the mandible of Geniohyux mirns, gen. et 

 sp. nov. Type -specimen. About two-thirds nat. size. 

 si/m. symphysis of mandible ; x, backwardly directed process on lower 

 border of mandible. 



III. — Note on the species ' Am. plicatilis ' and ' Am. biplex ' 



OP SOWERBY. 

 By Rev. J. F. Blake, M.A., F.G.S. 



THE old question of the proper interpretation of these names, 

 which was raised by Professors Nikitin and Pavlov, after 

 their visit to this country for the Geological Congress in 1888, 

 to whom no reply was made, for their conclusions could scarcely 

 be denied, has been raised again by Miss Healy in a communication 



