MEDUS.5. I. 



31 



Genus Ptychogena A. Agassiz. 

 Ptychogena lactea A. Agassi z. 



Plate III, figs. 1—6. Textfig 5. 



Ptychogena lactea A. Agassiz 1865. North American Acalephse, p. 137, figs. 220—224. 



— — Haeckel 1879. System der Medusen, p. 147. 



— pinjuilata Haeckel 1879. ^^^^- P- 148- 



— — — 1881. Tiefsee-Medusen der Challeiiger-Reise, p. 6. Taf. II. 



— lactea A. Agassiz 1888. Bull. Mus. Comp. Zool. Harvard Coll. Vol. XV, p. 128. 



— pinnulafa Levinsen 1892. Meduser etc. fra Gronlands Vestkyst. — Vidensk. Meddel. Natiir- 



hist. Foren., 1892, p. 145. 



— — Aurivillius 1896. Plankton der Baffins Ba\- nnd Davis' Strait. — Festskr. Wilh. 



Lilljeborg tillegnad, p. 198. 

 lactea Vanhoffen 1897. Fauna und Flora Gronlands. — Drygalski's Gronland-Exped. 

 Bd. II, p. 273. 



— pinnnlata Gronberg 1898. Hydroid-Medusen des arktischen Gebiets. — Zool. Jahrb. Bd. XI, 



p. 465. 



— — var. Linko 1904 b. Zool. Studien im Barents-Meere. — Zool. Anz. Bd. XXVIII, 



p. 217. 

 lactea Browne 1907. Revision of the LaodiceidcC. — Ann. Mag. Nat. Hist. Ser. 7. Vol. XX, 



P- 473- 



— — Mayer 1910. Medusae of the World, p. 215. 



— — Bigelow 1913. Medusae ... N. W. Pacific. — Proceed. U. S. Nat. Mus. Vol. 44, p. 28. 



— — Kramp 1913. Medusas . . . "Tjalfe" Exped. — Vidensk. Meddel. Dansk Naturhist. 



Foren. Bd. 65, p. 268. 



— — 1914- Conspectus F'aunEe Groenlandicae, p. 422. 



Description of a full-grown .specimen from the south coast of Disco, Greenland, "Tjalfe" 

 Exped. Stat. 125. 



Diameter (the specimen is preserved in alcohol) about 90 mm, height of the bell about 30 mm. 

 The gelatinous substance is very thick, 10 mm at the apical point; the thickness is almost equal 

 throughout the greater part of the bell; only in the peripheral part, within a short distance from the 

 bell-margin, it is evenly diminishing towards the latter. The stomach is quadrate, attached to the 

 subumbrella along the arms of a perradial cross, so that there are four interradial, triangular pouches 

 between the dorsal wall of the stomach and the subumbrella. The length of the sides of the stomach 

 is 20 mm. The prismatic mouth-tube is short, hardly 10 mm long. The mouth-opening is quadrate ; the 

 four perradial corners are dilatated into four quite short lips. The mouth-edge is faintly folded. The 

 perradial cross, mentioned above, along the arms of which the stomach is attached to the subumbrella, 

 is seen on the inner side of the dorsal wall of the stomach as four ciliated grooves; in this specimen 

 the grooves do not meet exactly in the centre (see Plate III, fig. i); the grooves are centripetal con- 

 tinuations of the dorsal wall of the radial canals. The proximal two-thirds of the 4 radial canals are 



