PALÉOZOOLOGIE ET PALEOPHYTOLOGIE 



73 



Negritos Formation. — The fauna consists mainly of Gasteropods and 

 Lamellibranchs, with a small number of Fish teeth, Decapod Crustacea, 

 Corals, and a species of Aturia. Several of the Mollusca show a graduai 

 change in character when traced through successive horizons. Thus in the 

 Venericardia planicosta group there is a steady decrease in the extent of the 

 development of the ribs. Several gasteropods show a progressive development 

 of callus until ultimately it covers the entire shell (Volutospina peruviana, 

 Pseiidoliva mutabilis, Strepsidura pacifica, Calyplrophorus Lissoni ). Most 

 of the species are pecuUar to the région, but their relationship indicates 

 interoceanic communication between the Pacific and the Atlantic in Eocene 

 times ; some resemble species found in he Wilcox and Lower Claiborne 

 Groups of the United States, and species in the Lutetian and Auversian of 

 France and England ; and a few are similar to species found in the Alpine 

 Middle Eocene (especially of Northern Italy) and the Eocene of Northern 

 Africa. The last is in accord with the affinities which hâve been noticed 

 between the Tertiary faunas of the West Indies and the Mediterranean 

 région. The Negritos Formation is considered to be represented by the 

 Wilcox and Lower Claiborne Groups of the U. S. A. (Lutetian and Auversian) 

 The foUowing species are found in the Negritos Formation : 



Corals : Paracyathus peruvianus, Oculina peruviana, Peruviasirse peru- 

 viana, Haimesiastrœa peruviana, H. humilis, H. distans, Slephanocœnia 

 peruviana, Dendrophyllia peruviana. 



Lamellibranchs : Leda ingens, Barbalia s p., Mylilus euglyphus, Ostrea 

 Inca, 0. Buski, Perna arbolensis, Venericardia planicosta (group), Callista 

 ( Macrocallisla ) Dickersoni, Meretrix Bosworthi, M. negritosensis, Cardium 

 sp., Corbula peruviana, C. Waringi, C. Arnoldi, C. parinasensis, Teredina sp. 



Gasteropods : Solarium Nelsoni, Ampullina Gabbi, Turritella negri- 

 tosensis, T. Dickersoni, T. Bosworthi, T. Douvillei, T. Lissoni, T. anceps, 

 T. annectens. Morgania magna, M. costata, Melanatria dimorphiea, M. 

 acanthica, M. propinqua, M. venusta, Pseudoglauconia Lissoni Douv., 

 « Cerithium » negritosense, « C. » Chatwini, Bezanqonia pupoidea, Potamides 

 «ecîdentalis, Diastoma americanura, Calyplrophorus Lissoni Douv., Pseudo- 

 liva parinasensis, P. mutabilis, Slrepsidura pacifica, Clavilithes Harrisi, 

 C. peruvianus, C. pacificus, C. incertus, Sycum amerieanum, Volutospina 

 peruviana, V. crassiuscula, V. meridionalis, Olivancillaria eocaBnica, Surcula 

 occidentalis, S. Thompsoni. 



Crustacea : Callianassa americana, Xanthopsis errans, Thaumasloplax 

 «ocsenicum. 



LoBiTOS FORMATION. — Fossils are less abundant and less well preserved 

 than in the Negritos Formation. The species found in the lowest 1000 feet 

 show a close connection with those of the preceding Clavilithes Séries ; 

 while those found at Lagunitas, the horizon of which is beUeved to be consid- 

 erably higher, are almost entirely différent from those of the Clavilithes 

 Séries. 



The species found in the Lobitos Formation and not in the Negritos For- 

 mation are : Lepidocyclina antillea, Cushm., L. ( N ephrolepidina ) peruviana, 



