Publicado por Paleontologia Mexicana no. 27, 1969, 88 pp., 1969
Librería: Eryops Books, Stephenville, TX, Estados Unidos de America
Soft Cover. Condición: Very Good. ORIGINAL PUBLICATION; Softcovers; ex-library; minor shelfwear w/ small creases at corners of wraps and pages; o/w in very good condition.