Albert D. Mahood

Chrysophyte cysts as potential environmental indicators.

Many Chrysophyte algae produce morphologically distinctive, siliceous, microscopic cysts during a resting stage of their life cycles; these cysts are often preserved in sediments. Scanning electron microscopy and Nomarski optics permit much more detailed observation of these cysts than was heretofore possible. We have used an ecologic and biogeographic approach to study the distribution of cyst forms in sediments and have established that many cyst types are found only in specific habitats, such as montane lakes, wet meadows, ephemeral ponds, and Sphagnum bogs. In the samples we have studied, cysts seem to be most common in fluctuating fresh-water habitats of low to moderate pH and some winter freezing. Numerous taxonomic problems have yet to be resolved. We believe that chrysophyte cysts have the potential to become a useful tool for both modern environmental assessments and paleoecological studies of Cenozoic fresh-water lacustrine deposits.

Stephanodiscus rhombus, a New Diatom Species from Pliocene Deposits at Chiloquin, Oregon

A new species of the diatom genus Stephanodiscus has been recovered from Pliocene freshwater deposits in the Klamath River basin at Chiloquin, Oregon. This new rhomboid-shaped taxon has been found in 3 closely related deposits: Terrebone, Oregon; Chiloquin, Oregon; and Pit River, California. It is clearly separated from a similar diatom, S. eccentrica Hustedt, by the rhomboid-shaped valve and other morphological details. Stephanodiscus rhombus, a new diatom species from Pliocene deposits at Chiloquin, Oregon

Aulacodiscus kittonii Arnott—distribution and morphology on the West Coast of the United States

The distribution and morphology of A. kittonii Arnott have been studied in samples from the Pacific coast of the United States. Size frequency distributions have been obtained for populations from beaches in Washington, Oregon, and California. Statistically significant differences in the mean diameter of valves from Copalis Beach, Washington; Doran and Scripps Beach, California exist. Mean diameters from the same or nearby beaches were not different even though in two instances six and 11 years elapsed between collections. The number of processes on 18,593 valves have been counted. The valves of this taxon characteristically possess four processes. Approximately 0·5% of the valves examined possess either three or five processes. Valves with no processes, one and two have been observed but are very rare. No valves with six, seven or eight processes have been observed. In frustules each valve normally possesses four processes. Frustules possessing one four-process valve and one with either three or five pro...

COMPARATIVE ULTRASTRUCTURE OF TWO CLOSELY RELATED THALASSIOSIRA SPECIES: THALASSIOSIRA VULNIFICA (GOMBOS) FENNER AND T. FASCICULATA HARWOOD ET MARUYAMA

The distinctive morphology and relatively short geological range (3.25 to 2.5 Ma) of Thalassiosira vulniflca (Gombos) Fenner make it especially useful for Pliocene biostratigraphic studies in the Antarctic region. Thalassiosira fasciculata Harwood et Maruyama has a geological range (4.5 to 0.75 Ma) that overlaps that of T. vulnifica and it resembles this taxon in possessing prominent fultoportulae on the valve face, strongly fasciculated areolae, and distinctive marginal fultoportulae. However, the greater spacing between rows of areolae and the larger distinctive fultoportulae present in T. vulnifica clearly separate it from T. fasciculata. The importance of accurate identification is discussed as it relates to ongoing Antarctic glacial sediment studies.

VULCANELLA HANNAE SIMS & MAHOOD, GEN. ET SP. NOV., WITH A DISCUSSION OF THE GENERA TUMULOPSIS HENDEY, ACANTHODISCUS PANTOCSEK, PORETZKIA JOUSÉ AND GONIOTHECIUM EHRENBERG

Vulcanella hannae gen. et sp. nov. is described and illustrated from the upper Eocene-lower Oligocene. This taxon has been illustrated by Gombos & Ciesielski (1983) as “species uncertain”, by Harwood (1989) as Cotyledon fogedi (Hendey) Harwood and by Barron & Mahood (1993) as Tumulopsis fogedi Hendey. The justification for establishing the new genus is supported by examination of the generitypes of Tumulopsis Hendey (T. fogedi) and Acanthodiscus Pantocsek (A. rugosus Pantocsek), together with species associated with or possibly related to the newly described taxon. Nomenclatural problems are discussed.

ENDICTYA HENDEYI SP. NOV., A NEW COASTAL DIATOM SPECIES FROM NORTH AMERICA

Endictya hendeyi E. Hemphill-Haley sp. nov. is described from Recent and Quaternary, estuarine and marine deposits along the west coast of the United States. This taxon is distinguished by its 1) consistently small valves; 2) areolae of uniform size on the valve face in linear tangential rows; 3) prominent, external spatulate extensions of the rimoportulae at the valve face/mantle junction; 4) externally projecting hyaline rim or flange at the interior edge of the mantle; and 5) discontinuous pattern of pores on the basal siliceous layer. The new species is compared to the generitype, E. oceanica Ehrenberg, as well as E. minor A. Schmidt and E. margaritifera A. Mann.