Reference on p. [528] n.
This account of the periproct is different from that ordinarily given. It is based on the most recent examination of this family—Agassiz, "Panamic Deep-sea Echini," Mem. Mus. Comp. Zool. xxxi. 1904, p. 36.
"Der Schatten als Reiz für Centrostephanus longispinus," Zeitschr. für Biol. xxxiv. 1896, p. 319.
Reference on p. [532], note [489].
Mr. E. W. L. Holt, Scientific Adviser to the Irish Board of Fisheries, casts doubt (in litt.) on much of this supposed excavation. While disclaiming any novelty in this observation, he points out that in many cases one side of the cavity is formed by calcareous algae, and it seems as if the animal wanders into a crevice, in which it is imprisoned by the growth of this plant.