ACADEMY OF NATURAL SCIENCES. 207 



iron ore is inter-stratified with chloritic and talcose slates and granite, and the 

 series also bears copper ores and gold. 



From the collections made by Lieut. Whipple's party, in 1853, in the mountains 

 north, it would appear, that similar rocks exist in the Cerbat and Aquarius 

 Mountains, the extreme geological antiquity of which, was commented on by me 

 in the Pacific R. R. Reports, Vol. Ill, p. 59. It is possible that this ferriferous 

 formation is connected with the extensive iron formation of the coast of Mexico, 

 south of Acapulco, described by Mr. Manross, (Am. Journ. Sci., XXXIX, 358,) 

 and it may be of pre-Silurian date. 



Descriptions of New Ttlarine Shells from the Coast of 



California. 



PART III. 



BY PHILIP P. CARPENTER, B. A., PH. D., OF WARRINGTON, ENG. 



Genus Corbui.a, Lam. (Auct.) 

 Corbula luteola, Cpr. n. s. State Collection, No. 587. 



C. t. " C. biradiatcc," format simulante, sed multo minore ; baud obesa, trans- 

 versa, lutoo-cinerea, dorsum versum interdum obscure biradiata ; angulo plus 

 minusve carinato, postice definite ; antice rotundata, expansa ; concentrice crebre 

 sed obtuse lirulata; umbouibus obtusis ; intus, dentibus minoribus ; linea pallii an- 

 gulata, haud sinuata ; cicatricibus adductoribus callosis ; margine t. adult& postice 

 altero alterum amplectante. 



Long. 0-42, lat. 0-28, alt. 0-16. 



Hab. San Diego, San Pedro, 50, alive, at low water. 



Genus Plectodon.* Cpr. 



Testa tenuis, scaber, rostrata, haud inflata : margo dorsalis sub umbones intus 

 nexa, dentem cardinalem formans : dentes laterales longi, laminati : cartilago foss& 

 minuta, sub umbones celata, dente laterali postico contigu&, sita : sinus pallii 

 parvus. 



Plectodon scaber, Cpr. n. s. State Collection, No. 1062. 



PI. t. ledce-formi, tenui, subdiaphauft, pallida ; tota superficie minute pustulosa • 

 marginibus dorsalibus rectis, ad angulum 150° ; antice et ventraliter producta, 

 marginibus excurvatis ; postice valde rostrata, truncata : intus, margine sub um- 

 bones interrupto ; plica ex apice oblique usque ad marginem dorsalem anticum 

 excurrente ; dentibus lateralibus laminatis, extantibus, postico longiore; cicatrici- 

 bus adductoribus parvis, subrotundatis, ad extremitates dentium lateralium sitis ; 

 sinu palii lato, haud impresso. 



Long. 0-62, lat. 0-34, alt. 0;20. - 



Hab. Catalina Island, two ri jht valves, 40-60 fms, Cp. 



* From the Greek, for twisted tooth 



