180 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



forms as Area grandis Broderip & Sowerby, Chione gnidia Sowerby, 

 Ostrea iridescens Gray, Pecten vogdesi Arnold, Pitar pollicaris Carpen- 

 ter, Plicatula spondylopsis Rochebrune, Pinctada mazatlantca Hanley, 

 Tivela byronensis Gray, Colubraria aphrogenia Pilsbry & Lowe, Conus 

 princeps Linnaeus, Conus orion Broderip, Fusinus dupetit-thouarsi 

 Kiener, Mitra attenuata Mawe, Strombus galeatus Swainson, Strombus 

 gracilior Sowerby, Strombus granulatus Mawe, Terebra lingualis Hinds, 

 Thais crassa Blainville, Thais kiosquiformis Duclos, Turritella banksii 

 Reeve, Vasum caestus Broderip. A number of species found in the 

 Recent west Panamanian fauna also occur in the Gulf of California 

 and range south to the Bay of Guayaquil. Certain of the species range 

 farther to the south. 



The surface temperature of the ocean near the shores of western 

 Panama from November to March was found by A. Agassiz^^ to be 

 between 80° and 82°F. The western Panamanian marine molluscan 

 fauna includes some species which also occur in the Caribbean Sea. The 

 exact number is not certain at the present time but several authors have 

 mentioned that about 50 species are common to the two areas. C. B. 

 Adams cited 21 species which he considered to be analogous to species 

 collected at Jamaica. It is certain that a much larger number of analo- 

 gous species than that given by C. B. Adams is present in the two 

 areas. The close relationship of the molluscan inhabitants of the Pana- 

 manian and Caribbean regions is readily explained by an open seaway 

 connecting the two areas which is believed to have existed during earlier 

 times. Such a connection is believed to have existed across the Isthmus 

 of Panama or some part of Central America at least during the lower 

 Miocene.-^ This made possible the migration of marine animals between 

 the two areas. Chione of the gnidia group, large Dosinia and Solenos- 

 teira became elements of the West American fauna at that time. There 

 is no evidence of any oceanic connection between the two regions since 

 the Miocene. Olsson^i in an excellent discussion of the Tertiary history 



19 Agassiz, A., Reports on the Scientific Results of the Expedition to the 

 Eastern tropical Pacific, in charge of Alexander Agassiz, bv the U. S. Fish Com- 

 mission Steamer Albatross, from October, 1904, to March, 1905. V. General 

 Report of the Expedition. Mem. Mus. Comp. Zool., vol. 33, 1906, pp. 25-26, pi. 3a. 



20 Dickerson, R. D., Ancient Panama Canals. Proc. Calif. Acad. Sci., sen 

 4, vol. 7, no. 8, 1917, pp. 197-205.— Smith, J. P., Proc. Calif. Acad. Sci., ser. 4, 

 vol. 9, no. 4, 1919, p. 129.— Hertlein, L. G., and Jordan, E. K., Proc. Calif. 

 Acad. Sci., ser. 4, vol. 16, no. 19, 1927, pp. 617-618. 



21 Olsson, A. A., Contributions to the Tertiarv Paleontology of Northern 

 Peru: Part 5, The Peruvian Miocene. Bull. Amer.' Paleo., vol. 19 (Bull. No. 

 68), June 30, 1932, pp. 41-43. 



