598 TIMOTHY WILLIAM STANTON 
the fauna until the extreme upper beds are reached, when a 
more abundant fauna appears that shows a blending with the 
succeeding Upper Cretaceous Chico fauna. These upper Horse- 
town beds have yielded the following species : 
Rhynchonella sp. © Mactra sp. 
Exogyra parasitica Gabb Pleuromya papyracea Gabb 
Pecten operculiformis Gabb Panopza concentrica Gabb 
Mytilus quadratus Gabb Lunatia avellana Gabb 
Mytilus cf. lanceolatus Sowerby Liocium punctatum Gabb 
Cucullzea truncata Gabb Acteonina californica Gabb 
Nemodon vancouverensis (Meek) Ringicula varia Gabb 
Leda translucida Gabb Desmoceras hoffmanni (Gabb) 
Trigonia equicostata Gabb Desmoceras cf. beudanti (Brongniart) 
Trigonia leana Gabb Haploceras brewer (Gabb) 
Meekia sella Gabb Lytoceras sacya Forbes 
Meekia navis Gabb Schloenbachia inflata (Sowerby) 
Meekia radiata Gabb Acanthoceras cf. mammillare 
Chione varians Gabb (Schloth.) 
Tellina matthewsonii Gabb Belemnites sp. 
After weighing the available paleontologic evidence and 
making all practicable comparisons with foreign Mesozoic fossils 
the conclusion was reached that the whole of the Knoxville is 
referable to the Neocomian and that the Horsetown includes all 
the rest of the Lower Cretaceous and possibly extends up into 
the Upper Cretaceous. 
The abundance of Aucelle gives the Knoxville fauna a decided 
boreal appearance, for the distribution of that genus has been 
considered essentially circumpolar. Some of the ammonitic 
types also point in the same direction, but the genera Lytoceras 
and Phylloceras are also represented, and these are the genera 
that Neumayr considered especially characteristic of the southern 
or tropical zone. With the disappearance of Aucella the fauna 
of the Horsetown becomes almost purely southern in type, so 
far as the ammonites are concerned, as Professor J. P. Smith* 
has stated; but this change can hardly be attributed to a change 
in climate, for it will be remembered that Aucella beds occur as 
tMesozoic Changes in the Faunal Geography of California, JouR. GEOL., Vol. 
III, 1895, pp. 381-382. 
