78 MR. H. WOODS ON THE MOLLT7SCA. [Feb. 1 896, 



being a little the smaller. After passing the inner tubercle the 

 ribs bend forward to the outer, and again forward to the carina. 

 The carina is strongly dentate, one tooth corresponding to each rib. 

 The ribs are of two sizes * ; the longer ones start from the umbilical 

 margin and bear there a small tubercle, but the smaller ones, which 

 alternate with these, begin a short distance from the margin and 

 do not bear at the starting-point a tubercle. 



Suture-line : the lobes and saddles not much divided, the saddles 

 much larger than the lobes. Siphonal saddle larger than the 

 superior-lateral and unsymmetrieally bipartite. Siphonal lobe 

 rather deep, divided by a saddle ; superior-lateral lobe larger than 

 the preceding and with unsymmetrical lobules ; inferior-lateral lobe 

 about half the size of the superior-lateral. 



Affinities. — This species is related to Ammonites Germari of 

 Reuss, 2 but is distinguished from it by the dentation of the carina 

 being much coarser. A. dentato-carinatus of Romer 3 differs from 

 this in having only one row of tubercles near the siphonal margin. 

 P. Neptuni is distinguished from the young forms of Ammonites 

 Woolgari, Mantell, by the greater breadth of the ribs. Sharpe 

 described and figured as Ammonites Bravaisianus, d'Orbigny, two 

 specimens from the Middle Chalk (probably Chalk Rock) of Dover, 

 which are probably identical with the species under consideration ; 

 the originals were in the collections of Mr. J. W. Flower and 

 Mr. S. J. Mackie, but I have not been able to see them. 



D'Orbigny's Ammonites Bravaisianus, from the ' gres vert supe- 

 rieur ' of Uchaux and Mondragon (Vaucluse), resembles P. Neptuni 

 in the form of the shell and the ribs, but the carina is entire. 

 D'Orbigny's types are preserved in the Palaeontological Laboratory 

 of the Paris Museum ; the largest has a diameter of 17 mm. The 

 figures given in the 4 Paleontologie Frangaise ' do not convey quite 

 a correct idea of the form of the ribs. 



Localities. — England : Chalk Rock of Oldborough Castle, Cuck- 

 hamsley, Prince's Risborough, Luton cutting, Dunstable, and Hitchin. 

 France : zone of Holaster planus in the Yonne, zone of Epiaster brevis 

 of Saint-Clement, zone of Terebratulina gracilis east of the Paris basin, 

 Senonian (F of M. Lambert) of Armeau. North-western Germany : 

 confined to the zone of Het. Reussianum, found at Bielefeld, Ringe- 

 berge, Heiningen, and Windmiihlenberge near Salzgitter. Saxony : 

 in the Mergelschichten (J. Brongniarti-heds) of Walkmiihle near 

 Pirn a ; Geinitz records one specimen from the Planer (Cenomanian) 

 of Plauen, near Dresden. Bohemia : Malnitz Beds, near Laun. 



1 In some specimens (e. g. PI. III. fig. 3) the difference in size of the ribs is 

 very slight. 



2 A. E. Reuss, ' Die Verstein. d. bohm. Kreide format.' 1845, p. 22, pi. vii. 

 f. 10. See also A. Fritsch and U. Schlonbach, ' Ceph. bohm. Kreideformat.' 

 p. 29, pi. xiv. f. 1, 2, pi. xvi. f. 7 ; and C. Schliiter, • Ceph. oberen deutsch. 

 Kreide,' p. 41, pi. xi. f. 15-17. 



3 F. Romer, • Die Kreidebild. v. Texas,' 1852, p. 33, pi. i. f. 2. 



