218 GENESIS OE THE ARIETIDyE. 



Lymense as described by Wright. The senile stages separate it from the last, 

 though it is probably closely allied, and might be considered a variety if occurring 

 in the same bed. Wright's Wiltshirei, which seems to be identical, was found in 

 the Henleyi bed of the Middle Lias. 



Second Subseries. 

 Oxynoticeras Greenoughi, Hyatt. 



Plate X. Fig. 30. Sumiu. PI. XIII. Fig. 13. 



Amm. Greenoughi, Sow., Min. Conch., II. p. 71, pi. exxxii. 

 Amm. Greenoughi, Hauek, Ceph. Nordostl. Alpen, p. 4G, pi. xii. 

 ,4mm. oxynolus, Haukr, Ibid., pi. xiii. fig. 6, 7 (not fig. 3, 4, 8, 9). 

 . Amaltheus Greenoughi, Wright, Lias Ammonites, p. 381, pi. xliv. 

 Amaltheus Guibalianus, Wright, Ibid., p. 385, pi. xlv. 

 Amm. Guilbalianus, D'Orr., Terr. Jurass. Ceph., p. 259, pi. lxxiii. 

 Amm. Guibalianus, Reyn^s, Plates (pars). 

 A mm. Guibali, Reyn^s, Ibid. 



The examination of German specimens led to the conclusion that this species 

 was closely allied to oxynotum in development and in sutures, and the splendid 

 suite of this species at Semur enabled us to solve all difficulties. 



Here also we were able to compare it with specimens of the true Collenoii, 

 D'Orb., the originals of which are in the Museum of Comparative Zoology, and 

 they have not the slightest claim to be considered identical. Oppel was probably 

 led astray by what he supposed to be the types in D'Orbigny's collection. 



Reynes has divided this species into three forms, not very readily distinguish- 

 able by their adult characteristics, but quite distinct when their development 

 and old age are studied. His principal observations on Lotharingus, Guibali, and 

 Greenoughi were made in the Museum at Semur. We however refer his Guibali 

 to Greenoughi, because of their close resemblance in development and old age, and, 

 in order to avoid the use of a new name, distinguish the next species, his Gui- 

 balianus, as Guibali. This also is justified by the types in the Semur collection, in 

 several of which these names are interchanged. The true Guibalianus, D'Orb., as 

 may be seen by comparison of the original specimen and the Semur collection, 

 has more abrupt umbilical shoulders, a more open umbilicus, less involute whorls, 

 and retains the keel and typical form of the whorls until a later stage of growth 

 than any of the group except oxynotum. 



The shell sometimes attains the size of 235 mm. before any marked change of 

 form is observable, and in one specimen reached the size of 410 mm. before the 

 keel disappeared. Finally, however, the keel begins to disappear, and eventually 

 all traces of it vanish in the rounded abdomen. The form, however, seldom 

 changes as completely as in Guibali. The length of the ribs, whether they are 

 all long or alternately long and short, is a characteristic of great variability, and 

 is of no use in distinguishing the species. 



There are. so far as we have seen, no representatives of this subseries in the 

 South German basin, and this observation is sustained by Quenstedt's " Ammo- 

 niten des Schwabischen Jura," which does not contain a single undoubted form 



