3518. Algae. 43 Color Photomicrographs. 1. Oscillatoria, thin section 2. Nostoc 3. Anabaena 4. Scytonema 5. Rivularia 6. Chroococcus 7. Gloeocapsa small colonies 8. Diatoms, different forms 9. Pleurosigma angulatum, surface of shell 10. Pleurosigma angula