Hn.i.KriN. S'o. Cai.ii . AcAiiKM > oi Siiimis XHl II, l';iri l. mir. THE ACTEOCINA OF SALTON SINK, COLORADO DESERT. CALIFORNIA l')\ ( i. \\ II I.F.TT Las .hn/rlrs Coiiiily Mvsciiin The fact that the Colorado Desert was formerly connected witli what is now tlic Gulf of California is generally accepted by geologists. Tn the book "The Salton Sea." by D. T. INIacDougal and collaborators (Carnegie Inst., Wash., 1914), W. P. Blake states (p. 3) that the Salton Sink and contiguous territory was covered by the ocean in Middle Tertiary. According to E. S. Free (op. cit. : 26), the sea was absent from the lower part of the sink in late Tertiary, and also just previous to the post-Tertiary u]>Iift. but there was a long intermediate period of which nothing is known. During this latter period there may have been a marine occupation, followed by the building up of the Colorado River delta and consequent shutting out of the sea. The Tertiary sea has left numerous Miocene fossil marine deposits in the Carrizo Creek region and other localities, but the common molluscan fossils (or subfossils) found in the immediate vicinity of the present Salton Sea are evidently of Quartenary age. and are almost entirely typical of fresh water. R. E. C. Stearns (Proc. U. S. Nat. Mus.. 24(1256), 1901: 287), in discussing this latter fauna, mentions having taken near Indio specimens of Tagelus and a single example of Ocinehra (Tritonalia ) poiilsoni Xuttall. Nothing is said regarding the con-dition or apparent age of these marine shells, but it would appear probable that they were not living at the same time and in the same locality as such fresh-water genera as Anodonta, Helisoma and Pahidestrina, the common members of the fauna in the near vicinity of Salton Sea. It is entirely possible that the Tagelus and Tritonalia may have washed down from an earlier deposit at higher levels. However, one supposedly marine genus has been found with the fresh-water genera by several collectors on different occas-ions, under conditions and in a state of preservation which appear to me to indicate that it might have been contemporaneous with the fresh-water fauna. This is the genus Acteocina (Tornatina of some authors, Retiisa of others). 28
BioStor
