13. The Pacific Coast Jays of the Genus _Aphelocoma_, by H. S. Swarth. Pp. 405-422, 1 figure in text. February 23, 1918 .20 14. Six New Mammals from the Mohave Desert and Inyo Regions of California, by Joseph Grinnell. Pp. 423-430. 15. Notes on Some Bats from Alaska and British Columbia, by Hilda Wood Grinnell. Pp. 431-433. Nos. 14 and 15 in one cover. April, 1918 .15 16. The Subspecies of the Mountain Chickadee, by Joseph Grinnell. Pp. 505-515, 3 figures in text. May 4, 1918 .15 Vol. 18. 1. Mitosis in _Giardia microti_, by William C. Boeck. Pp. 1-26, plate 1. October, 1917 .35 2. An Unusual Extension of the Distribution of the Shipworm in San Francisco Bay, California, by Albert L. Barrows. Pp. 27-43. December, 1917 .20 3. Description of Some New Species of _Polynoidae_ from the Coast of California, by Christine Essenberg. Pp. 45-60, plates 2-3. October, 1917 .20 4. New Species of _Amphinomidae_ from the Pacific Coast, by Christine Essenberg. Pp. 61-74, plates 4-5. October, 1917 .15 5. _Crithidia euryophthalmi_, sp. nov., from the Hemipteran Bug, _Euryophthalmus convivus_ Stål, by Irene McCulloch. Pp. 75-88, 35 text figures. December, 1917 .15 6. On the Orientation of _Erythropsis_, by Charles Atwood Kofoid and Olive Swezy. Pp. 89-102, 12 figures in test. December, 1917 \ .15 7. The Transmission of Nervous Impulses in Relation to Locomotion in the Earthworm, by John T. Bovard. Pp. 103-134, 14 figures in text. January, 1918 .35 8. The Function of the Giant Fibers in Earthworms, by John F. Bovard. Pp. 135-144, 1 figure in text. January, 1918 .10 9. A Rapid Method for the Detection of Protozoan Cysts in Mammalian Faeces, by William C. Boeck. Pp. 145-149. December, 1917 .05 10. The Musculature of _Heptanchus maculatus_, by Pirie Davidson Pp. 151-170, 12 figures in text. March, 1918 .25 11. The Factors Controlling the Distribution of the Polynoidae of the Pacific Coast of North America, by Christine Essenberg. Pp. 171-238, plates 6-8, 2 figures in text. March, 1918 .75