Yol. 69.] JURASSIC AMMONITES FROM JEBEL ZAGHTJAN. 553 



belonging to this group. The ventral area is carinatisulcate on 

 the last whorl ; the penultimate one is more rectangular, with a 

 tabulate periphery and a high keel, which is probably hollow, 

 although the crystalline infilling does not let this character show 

 itself very clearly. The inner whorls are much compressed and 

 oval-lanceolate in section, with an acute periphery. The umbilicus 

 is wide (the inclusion being rather less than a quarter) with well- 

 defined perpendicular walls, but a rounded border. 



The ornament consists of very close costse, which seem to de- 

 generate into irregular striae towards the end ; both have a very 

 distinct bend at the inner third of the side (subanguliradiation), and 

 the outer part of the radial curve is somewhat rursiradiate, has 

 only slight peripheral projection, and becomes indistinct before 

 reaching the ventral area. This kind of ornament is limited to the 

 outer whorls only, however ; before then the ribs are much stronger 

 and more distant, and, finally, disappear altogether on the inner 

 whorls. 



The suture-line is, unfortunately, not clearly visible, but seems 

 to agree with that of the type. 



The form here described differs from Dr. Tausch's form in the 

 larger umbilicus (46 per cent, of the diameter instead of 42) and 

 in the beginning of degeneration of the ornament. 



The form which Dr. Rosenberg figures comes very near to the 

 type, and his section 2 b (pi. xvi) agrees well with that of my 

 specimen. The costation is also too prominent ; and, moreover, it 

 is probably exaggerated, so far as the lateral bend is concerned. 



The ammonite figured by Wright has little affinity with A. d'Or- 

 bigny's Ammonites normanianus, as has been pointed out by 

 several authors. Dr. Geyer 1 thinks that it probably belongs to 

 a form of the boscense group, and Fucini compares it with his 

 variety ins&parabile of ' Grammoceras ' normanianum (d'Orb.) since 

 their dimensions agree. Dr. Tausch, on the other hand, says 

 that "Wright's form is distinguished from Harpoceras comacaldense 

 Tausch only by its section, which is thicker (20 per cent, of the 

 diameter). According to my measurements on the specimen pre- 

 served in the British Museum (Natural History), the umbilicus is 

 42 per cent, of the diameter : that is, the same as in H. coma- 

 caldense. The ornament is, however, stronger and very regular; 

 it consists of eighty-five costee on the last whorl, and only near 

 the end (of a specimen measuring 30 mm. more in diameter than 

 the shell here described) does degeneration set in. A new name, 

 Protogrammoceras wrighti, nom. nov. ( = Harpoceras nor- 

 manianum Wright non d'Orb. 2 ), may well be proposed for this 

 ammonite. I may here add that Wright's figure is not quite 

 correct. The radial line should indicate the lateral angularity at 

 the inner third, and the inner whorls, which are smooth at first, 



i ' Mittelliasisohe Cephal.Fauna des Hinter-Schafberg' Abhancll. K.K. Geol. 

 Eeichsanst. vol. xv, pt. 4 (1893) p. 18. 



2 'Lias Ammonites' Monogr. Pal. Soc. (1878-86) p. 470 & pi. lxxxiii, 

 figs. 1-2. 



