TMETOCERAS. 
269 
■when it appeared. It is nearest to PolyynorpJiites norma (Dumortier) ;^ but its 
compressed, quicker-coiled whorls separate it effectually from that, and from all 
the other species of the genus. 
I have only the one specimen which is figured. I collected it at Haresfield 
Hill from the bed containing Terebratula Jiaresfieldensis (bed 19, p. 44< ; see also 
p. 166) ; and its horizon is therefore the very top of the Jurense-zone (Dumor- 
tieria-beda). 
This little species is depicted in PL XL VIII, figs. 13 — 15. 
PoLYMOEPHiD^ {continued). 
Genus — Tmetoceeas,^ 8. BucJcman. 
{Type — Tmetoceras scisstrar, Benecke sp.) 
Discoidal, compressed, ventrally-sulcate. Whorls ornamented with annular or 
subannular ribs which produce a blunt knob on the ventral area, where they are 
interrupted rather suddenly. Suture-line simple ; superior lateral lobe about as 
long as siphonal ; one auxiliary lobe ; inner lobes not retracted. 
The generic classification and the genealogic connection of " Am. scissus " have 
been matters upon which there is, and has been much diversity of opinion. 
Neumayr^ put the species in the genus Simoceras with a query ; I placed it in the 
genus Gosmoceras ZitteP located it in the genus ParJcinsonia, and stated 
that it was the oldest representative thereof ; Vacek" relegated it to the genus 
Simoceras together with Am. Bumortieri ; while Haug'' returned it to the genus 
ParJcinsonia, not only endorsing Zittel's view that it was the oldest form of the 
genus — in fact, the ancestor from which the Parldnsoniae were derived, but that 
it was intimately connected genetically with Am. Bumortieri, and was, in fact, 
the connecting link between ParJcinsonia and Bumortieria (CatuUoceras). 
Simoceras is, according to Zittel, a genus belonging to the top of the Upper 
Jura ; and it is not only very different in appearance, but, from what is known of 
other Ammonites, is most unlikely to have any close genetic connection with 
^ ' Bassin du Ehone,' iv, pi. Ivii, figs. 7, 8. 
^ TuTjTus — furrowed. 
^ 'Unverm. Auftr. Ceph.;' Jahrbuch k.-k. geol. Eeichsanstalt, Band xsviii, Heft 1, p. 71, 1878. 
* New Amm. ; ' Proe. Dorset jST. H. See.,' vol. iv, p. 141, 1883. 
5 ' Handb. Pal.,' Bd. i, Abth. 2, Lief. 3, p. 472, 1884. 
® ' Ool. Cap. San Vigilio ;' Abb. k.-k. geol. Eeichsanstalt, Bd. xii, No. 3, p. 103, 1886. 
" Polymorphidse," ' Neues Jabrbuch fiir Mineralogie,' Bd. ii, p. 151, 1887. 
