. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. Section I. Description of the species. Subtribus Protactininae. Family Gonactiniidae. Diagnosis: Protactininae with flattened, disclike, proximal body-end. Column of the same struc- ture as the tentacles with spirocysts and a more or less strongly developed, longitudinal muscle- and nerve- layer, not capable of involution. No distinct sphincter. lyongitudinal muscles of the tentacles ectodermal (in Gonactinia sometimes with a little tendency to be meso-ectodermal?) even as the radial muscles of the oral disc. Actinopharynx n
. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. Section I. Description of the species. Subtribus Protactininae. Family Gonactiniidae. Diagnosis: Protactininae with flattened, disclike, proximal body-end. Column of the same struc- ture as the tentacles with spirocysts and a more or less strongly developed, longitudinal muscle- and nerve- layer, not capable of involution. No distinct sphincter. lyongitudinal muscles of the tentacles ectodermal (in Gonactinia sometimes with a little tendency to be meso-ectodermal?) even as the radial muscles of the oral disc. Actinopharynx not rudimentary, with longitudinal muscles and often with spirocysts, with weak siphonogl)q)hes or without. Mesenteries typically arranged in cycles, each pair of mesenteries, except the directives, with the longitudinal muscles facing each other. 8 (the ";), 10 or 12 mesenteries perfect. Reproductive organs arranged in the usual manner, as a rule on all perfect mesenteries. Muscles of the mesenteries weak, especialh- the parieto-basilar nmscles. No ciliated lobes to the mesenterial filaments. Stomata absent or only the oral stomata present. In this family I have previously (1900) placed the genera Protanthea, Gonactinia and preliminarily also Boloceroides. Concerning the last genus, which has formerly been referred to the Boloceriidae, its affi- nity with Protanthea and Gonactinia has been admitted by Pax (1914 p. 608) and Poche (1914 p. 97), whereas Mc. Murrich (1904 p. 255) and later Stephenson (1918 p. 6) have not accepted it as belonging to the family Gonactiniidae. These latter authors, however, ha\-e not given any important arguments for their point of \'iew, no more have they refuted my objections against the affinity of the genus with the Bolo- ceriidae (vide Carlgren 1911). As I have pointed out, one of the differences between Protanthea and Go- nactinia on one side and Boloceroides on the other is that the former are devoid of ciliated
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