372 MEDUSA OF THE WORLD. 



In 1879, 1881, Haeckel established the family Pectyllidae for his genera Pectyllis, Pectis, 

 and Pectanthis. Browne, 1903, and Maas, 1906, have shown that Haeckel's account ot 

 Pectyllis is very erroneous, that his three genera are probably only one, and that Allman's 

 generic name Ptychogastria takes precedence over Pectyllis Haeckel. The details of these 

 corrections will appear in the following account of the species. 



Genus PTYCHOGASTRIA Allman, 1878. 



Ptvchogastiia, Allman, 1878, Hydrozoa, in Nare's Narrative of Voyage to Polar Sea in H. M. S. Alert and Discovery, vol. 2, 

 p. 290.— Browne, 1903, Bergens Museums Aarbog, No. 4, p. 24. — Maas, 1906, Fauna Arctica, Bd. 4, Lfg. 3, p. 492, 

 Jena; 1906, Expedition Antarctique S. Y. Belgica, Medusen, p. 7, Anvers. 



Pcctyl/is + Pectis + Pectanthis, Haeckel, 1879, Syst. ^ er Medusen, pp. 265, 266, 267. 



Pectyliss+ Pectis-\- Pectanthis, Haeckel, 1881, Deep-sea Medusae, Challenger Report, Zoo]., vol. 4, pp. 10, 15, 19. 



The type species is Ptychogastria polaris Allman = Pectyllis arctica Haeckel, of the Arctic 

 Ocean. 



GENERIC CHARACTERS. 



Trachymedusae with numerous isolated clusters of tentacles upon the bell-margin. 

 These tentacles arise in several rows and some of them are provided with suckers, while others 

 lack these appendages. Isolated, single tentacles may arise from the margin between the 

 tentacle-clusters. 8 radial-canals. The ring-canal may give off blindly ending centripetal 

 branches. Mouth quadratic, with 4 lips. The base of the stomach gives rise to 8 lobes, 

 continuous with, and in the radii of, the 8 radial-canals, and these lobes are bound to the 

 subumbrella wall by arch-like mesenteries. The 8 more or less completely cleft gonads are 

 developed upon these stomach-lobes and are more or less separated by the 8 mesenterial 

 partitions, so that there may be 8 double ( = 16) gonads. There are sensory-clubs upon the 

 bell-margin. 



The differences between the genera "Pectyllis," "Pectis," and "Pectanthis," as defined 

 by Haeckel, are so slight as to appear of specific rather than of generic value; moreover, 

 Pectyllis Haeckel is certainly identical with the older genus Ptychogastria Allman. 



Admirable as Haeckel's system of the medusae is, it appears to me that it lays so much 

 stress upon pointing out distinctions that relationships are frequently obscured. I believe, 

 however, that the chief object of a system should be to indicate relationships; I have, there- 

 fore, presumed to broaden the definitions of many of Haeckel's genera, thus greatly reducing 

 their number and bringing closely related forms into closer contiguity one with another in the 

 text, instead of widely separating them, as is often done by Haeckel. From the nature of 

 the conditions, however, these matters are more or less subjective, and one's own opinion 

 changes from time to time even though the data for the definitions of related genera remain 

 the same. It is fortunate for science that with the discovery of the law of evolution the old 

 importance of systems 'fell to the ground, and to-day systems are of service only in the 

 proportion that they indicate the blood-relationships of forms and present a logical and con- 

 venient means of classification. 



Ptychogastria polaris Allman. 



Ptychogastria polaris, Allman, 1878, Hydrozoa, in Nare's Narrative of Voyage Polar Sea in H. M. S. Alert and Discovery, vo\. 

 2, p. 290, 3 figs. — Browne, 1903, Bergens Museums Aarbog, No. 4, p. 24, plate 4, figs. I, 2; plate 5, figs. 6-8. — Maas, 

 1906, Fauna Arctica, Bd. 4, Lfg. 3, pp. 482, 492, 509 (description of medusa and review of literature). — Linko, 1904, 

 Zool. Anzeiger, Bd. 28, p. 218.— Broch, 1907, Report of the Second Norwegian Arctic Expedition in the Fram, No. 12, p. 8. 



Pectyllis arctica, Haeckel, 1879, Syst. der Medusen, p. 266; 1881, Deep-sea Medusa?, Challenger Report, Zool., vol. 4, p. II, 

 plates 3, 4.— Maas, 1893, Ergeb. der Plankton Exped., Bd. 2, K. c, p. 20— Gronberg, 1897, Zoolog. Jahrb., Abth. Syst., 

 Bd. II, p. 465. — Linko, 1900, Soc. Imp. des Naturalistes Travaux, tome 31, p. 117. 



Bell hemispherical or more or less conical, with a bluntly rounded, aboral apex. 10 to 15 

 mm. wide, 9 to 12 mm. high. According to Haeckel and Maas, there are 16 projecting radiat- 

 ing ribs on the exumbrella, alternating with 16 deep grooves. According to Browne, the exum- 

 brella displays "numerous longitudinal ridges," but he does not state their number. Velum 

 very wide, probably capable of nearly closing the opening of bell-cavity. Bell-margin is 

 thickened and beset with about 48 clusters of tentacles; each cluster arises from a triangular 

 thickening upon bell-margin; the tentacles of each cluster are of two sorts and are definitely 



