N.  Eldredge and Gould, S. Jay, ?Punctuated equilibria: an alternative to phyletic gradualism?, in Models in paleobiology, T. J. M.  Schopf, Ed. San Francisco: Freeman, Cooper, 1972, pp. 82-115.

N.  Eldredge, ?Systematics and evolution of Phacops rana (Green, 1832) and Phacops iowensis Delo, 1935 (Trilobita) from the middle Devonian of North America?, Bulletin of the American Museum of Natural History, vol. 147, pp. 47-113, 1972.