600 



S. S. BTJCKMAN ON AMMONITES PROM 



The true C. Parlcinsoni occurs in great numbers at Halfway House, 

 also at Bradford Abbas, Burton Bradstock, and Sherborne, 



The variety rarecostatum, S. S. Buckm., occurs in the same beds 

 at Sherborne, Bradford Abbas, Burton Bradstock, Broad Windsor, 

 &c, but is not so common. 



Cosmoceras Parlcinsoni is characteristic of the upper beds of the 

 Inferior Oolite. The very adult forms lose all their ribs and also 

 the division on the ventral area, and are very different from the 

 ordinary young form which was figured by Sowerby. 



Bayle has separated this species from the genus Cosmoceras under 

 the generic name of Parkinsonia. I am rather of opinion that it, 

 and also Cosm. Caumontii (d'Orb.), should be so separated. 



The termination of this species is somewhat produced on the ven- 

 tral area. I possess one specimen with the termination on the outer 

 half of the whorl well shown, but am unable to say whether the 

 species possesses a horn on the side, or merely a plain double curve. 

 Length of body-chamber -| of a whorl. 



Cosmoceeas Caumontii (d'Orb.). 



Ammonites Caumontii, d'Orb. Terr. Jurass. pi. 138. figs. 3, 4. 



Locality. It occurs at Oborne in the zone of Stephan. Humphriesi- 

 anum, but is scarce. 



The termination is merely a small, very thin, narrow ear. 



Cosmoceras Garantiantjm (d'Orb.). 



1845. Ammonites Garantianns, d'Orb. Terr. Jurass. pi. 123. 



1849. A. Parlcinsoni clubius, Quenstedt, Ceph. tab. ii. fig. 9. 



1854. A. Garantianns (d'Orb.), Morris, Catalogue, p. 292. 



1856. A. Garantianns (d'Orb.), Oppel, Juraforroation, p. 381, 

 no. 53. 



Localities. Humphriesianum zone, and less commonly in the lower 

 part of the Parlcinsoni zone, Oborne, Louse Hill, Wyke : rather 

 common. 



The termination is a semilunar band. 



Cosmoceras stjbetjrcatum (Schlotheim). 



1830. Ammonites subfurcatus (Schlotheim), Zieten, Yerst. Wiirt- 

 temb. pi. vii. fig. 6. 



1845. A. niortensis, d'Orb. Terr. Jurass. pi. 121. figs. 7-10. 



1849. A. Parlcinsoni bifurcatus, Quenstedt, Ceph. tab. ii. fig. 11. 



1856. A. subfurcatus (Zieten), Oppel, Juraform. p. 381, no. 52. 



Zieten figures this species, giving Schlotheim as the authority for 

 the name. 



Zieten's figure shows a fossil with a large number of bifurcating 

 ribs, which is the exception and not the rule, this species usually 

 having very few bifurcating ribs, as is shown by d'Orbigny, who 

 figured it under the name of A. niortensis. 



[There is also a fossil, of which a few specimens have occurred 

 at Oborne, which is probably a variety of this species. It has very 



