1916] 



Dickerson: Tejon Eocene of California 



477 



Solarium alveatum Conrad 

 Solarium amoenium Conrad 

 Trigonoarca decisa Conrad 

 Actaeon idoneus Conrad 



= Area hornii Gabb 

 cf. A. moodyi, n. sp. 



cf. Architectonica cognata Gabb 

 = Architectonica hornii Gabb 



Durable 00 found an interesting Eocene locality at Topila, Mexico, 

 Gulf Coast. At a depth of 1800 feet several shells were brought up in 

 the oil-drilling operations. Among them were the following Tejon 

 species: Orbitoides, sp., Neverita cf. secta Gabb, Dentalium strami- 

 neum Gabb, Conus remondii Gabb, Conns calif orniana (Conrad), 

 Turris monolifera (Cooper), Drillia, cf. ullreyana Cooper, and Turri- 

 tella cf. kewi, n. sp. 



Unfortunately most of these similar or identical species are forms 

 with very great stratigraphic range in both the Tejon and the Gulf 

 Eocene. Natica, Modiolus, Caclulus, Calyptraea, Olivella, Olivula are 

 particularly poor genera for correlation purposes, as specific and 

 individual differences are not sharply marked and individual varia- 

 tion is great. 



The occurrence of Whitneya ficus Gabb in lower Claiborne strata 

 of Texas, Solarium alveatum Conrad and Solarium amoenium Conrad 

 md a subspecies of V enericardia planicosta which is the equivalent of 

 V. planicosta hornii (Gabb) in the Claiborne of Alabama suggests that 

 the Rimella simplex zone, the fauna of the type Tejon, is the equiva- 

 lent of the Claiborne or lower Claiborne. 



Stages of Evolution of the Species Venericardia Planicosta Lamarck 



The mutations of Venericardia planicosta Lamarck are very sug- 

 gestive. The important changes in this species, both on the Pacific 

 and Gulf Coasts, is a progressive alteration in the strength of radial 

 ribs and their interspaces and a similar acceleration of development. 



V. planicosta venturaensis (Waring) is a higher form than 

 V. planicosta smithi (Aldrich) of the Midway stage but the inter- 

 spaces and ribs have the same relative width and development. 



V. planicosta hornii Gabb which occurs in the Turbinolia, Rim- 

 ella simplex and Balanophyllia zones of the Tejon group corre- 

 sponds in the lessening width of interspace with V. planicosta, 

 form a Harris 91 of the lower Lignitic. V. planicosta merriami 

 Dickerson of the Siphonalia sutterensis zone corresponds to V. 



bo Dumble, E. T., Science, new series, vol. 35, pp. 906-908, 1912. 

 si Harris, G. D., The Lignitic Stage, Bull. Amer. Pal., vol. 2, No. 9, 

 pp. 246-247, 1897. 



