34 



CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Upper Chico Forms. 



Pachydiscus 7iewberryanus 

 Schloenbachia chico'insis 

 Schlcenbachia gahbi 

 Aiichura fakifonnis 

 Eripachya pofiderosa 

 Fulgur hilgardi 

 Fiilguraria gabbi 

 Gyrodes expansa 

 Perissolax brevirostris 

 Tnrritella chicoensis 

 Turritella robusta 

 Tellina sp. 

 Meekia sp. 

 Anoviia sp. 

 Lntraria iritncata 

 Lucina sp. 

 Trigonia evansana 

 Pecfuncuhis veatchi 

 Venus veatchi 



Lower Chico Forms. 



Lytoceras sacya 

 Ly toe eras j acksonense 

 Lytoceras jukesi 

 Placenticeras pacifictiin 

 Placenticeras caltforn icu m 

 Phylloceras rarnosum 

 Nautilus sp. 

 Prionotropis sp. 

 Scaphites sp. 



Schl(£7ibachia oregonensis 

 Schlcenbachia in nit i cost a 

 Schloenbachia propinqua 

 Schloenbachia siskiyouensis 

 ActcEon pugilis 

 Actcsonella oviformis 

 Actceonina californica 

 ActcBonina pupoides 

 Antanropsis alveata 

 Anchura californica 

 Anchura condoniana 

 Inoceramus labiatus 

 Inocerainus xvhitneyi 

 Lima appressa 

 Lima microtis 

 Nemodon vancotiverense 

 Pecten operculiformis 

 Pinna breweri 

 Pleuromya Icsvigata 

 Protocardium scitulnni 

 Trigonia rel. T. evansana 

 Trigonia leana 

 Thetis aimnlata 



Considering, then, the Lower and the Upper Chico, it 

 will be seen not only that there is a quite noticeable devel- 

 opment of gastropod and bivalve species in passing from 

 Lower to Upper, but there is also a large omission of former 

 species and genera and their replacement by others of 

 usually different groups. For example, of the many species 

 of cephalopods found in the Lower division, only four have 

 been thus far reported from the Upper; and only two with 

 certainty of identification. Among the gastropods only 

 eleven have been reported as common to the two horizons 

 and some of them are likewise doubtful. Others, as Gyrodes 

 expansa and Cinulia obltqua, are forms that might easily be 



