a YORKSHIRE TYPE AMMONITES Dec. 



Genus, AGASSICERAS, Hyatt, 1875 



1875, New Gen. Amm. ; Proc. Boston Soc. Nat. Hist. XVII, 225. 



In his original description of the genus, Hyatt included three species, 

 Am. Icevigatus, J. de C. Sowerby, Am. striaries, Quenstedt, Am. scipioni- 

 amis, d'Orbigny. The first of these would fall into the genus Cymhites, 

 Neumayr, 1878 ; and for the last Hyatt has erected a genus Mtomoceras 

 (1900, Eastman-Zittel, 575). This leaves Am. striaries as the type ; 

 and the comparable species mentioned in p. 6c., with A. resupinaius, 

 appear to be stout developments of a siriaries-like form. Mtomoceras 

 is the thin development from a similar stock. 



In discussing such species — Geol. Mag. (4) I, (1894), 359 — I suggested 

 that Am. scipionianns might be taken as the type of Agassiceras, and 

 ranged A. sauzeanus with it ; but Hyatt preferred to make a new genus 

 for A. scipionianus. He did not see the relationship of A. sauzeanus 

 with the striaries and scipionianus series ; for he placed it in Coroniceras — 

 Gen. Ariet. ; Smithson. Contrib. 673 (1889), 184 ; but the deficiency of 

 channels and the Asteroceras pattern of lobes remove A. sauzeanus and 

 its allies from Coroniceras. 



Genus, OXYNOTICERAS, Hyatt, 1875 



1875, New Gen. Amm.; Proc. Boston Poc. Nat. Hist. XVII, 230. 



According to the etymology, A. oxynoius, Quenstedt, must be taken 

 as the type. For a treatise on the species of the genus see Pompeckj, 

 Com. Serv. Geol. Port., vi, ix)o6, 214. 



The many Liassic species assigned to the genus are so diverse in 

 character that they are probably polyphyletic — Quart. Journ. Geol. Soc, 

 Liv, 1898, Table 11, facing p. 451, and p. 453. 



The A. oxynotus-series is probably a lateral branch from Agassiceras, 

 through stages akin to Asteroceras. This is close to Pompeckj's result 

 (P- 333)> but see S. Buckman, Mon. 1889, 226, and 1898 op. cit. above. 



A. oxynoius, which is a phylogerontic form of the series, shows 

 remarkable saltative palingenesis. Its ornament-record would be, in 

 phylogeny, i, 2, 3, 4, 5, 4c, 3c, but its ontogeny is often i, 3c, a skipping 

 of five stages. See also Pompfxkj, 286. For evidence as to stage 5 in 

 Oxynoticeras, see A. dennyi, No. 7. 



Genus, HARPOCERATOIDES, nov. 

 Type, Am. alternatus, Simpson (see No. 9). 



The rib-curve is subfalciform, not strongly geniculate ; the ribs 

 are bundled on the inner area in a wavelike manner ; the umbihcal 

 edge is bevelled, tendmg to concave ; there is a small septicarina. 



The rib-curve, the bundling of the ribs, and the inner margin bevelled 

 instead of undercut, separate this genus from Harpoceras : the less 

 falciform radial line, with less distinct angulation in the lateral area, 

 is especially noticeable. 



Of the Comparable Species in page 9c, A. strangewaysi and H. 

 kisslingi belong here; A. ovattis has similar rib-curve, but a different 

 suture-line. 



