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SUMMARY Electron microscope investigations of the siliceous frustule show that the diatom described by Hustedt as Stephanodiscus subsalsus (A. Cleve) Hust. is not Skeletonema subsalsum (A. Cleve) Bethge (Melosira subsalsa A. Cleve) but is Microsiphona potamos Weber. This species is so similar to Skeletonema costatum (Grev.) Cleve and Skeletonema subsalsum that the combination Skeletonema potamos (Weber) Hasle is suggested. Present records classify Skeletonema potamos as a freshwater species of lakes and rivers. In Sandusky Bay, Lake Erie (U.S.A.) and in River Wumme, a tributary of the River Weser (Germany) it grows with Skeletonema subsalsum. In nature, and when grown in cultures at a salinity of 0%, the processes are extremely short; when grown at salinities of 2% or more, the processes are much longer.

The absorption, excretion, and biotransformation of 14C-diphenoxylate hydrochloride (5 mg. containing 20.2 µc of 14C) when administered orally in ethanolic solution and without the presence of atropine sulfate was studied in 3 men. The mean urinary and fecal excretion of the total label in a 96 hour period was 13.65 ± 1.18 per cent and 49.20 ± 2.24 per cent, respectively. Thin-layer radiochromatographic analysis of the label in excreta indicated extensive biotransformation of the parent drug. In the urine, the maior metabolites were characterized as diphenoxylic acid and hydroxydiphenoxylic acid. These acids were present in both the free and coniugated fractions. Radioactivity in the plasma was associated largely with diphenoxylic acid and to a smaller extent with the unchanged drug. Pharmacokinetic analysis using a one-compartment open model showed a rapid absorption (t½ = 19.7 ± 1.7 minutes; peak level at 2.0 hours) of diphenoxylate followed by its rapid elimination (t½ = 2.50 ± 0.34 hours). The plasma half-life (t½ = 4.38 ± 1.04 hours) of diphenoxylic acid was higher than that of diphenoxylate.