MEDUSA. I. 



35 



nearly circular in outline, as jn the specimen from the Kara Sea (locality No. 9) and the 70 mm wide 

 specimen from the "Tjalfe" stat. 125, or it may be more lengthened, elliptical. 



From the "Tjalfe" stat. 171 we have a specimen, 50 mm wide, in which the canal system is 

 abnormally developed. One of the radial canals is bifurcate proximally near its point of issue from the 

 stomach. Each of the two branches has its own system of lateral branches and gonads, and the two 

 systems do not touch each other. The one system is somewhat smaller than the other and diverge 

 somewhat more from the perradial direction. This "secondary" canal has, probably, not reached to the 

 circular vessel; this cannot, however, be stated with certainty. The gonads in the "secondary" system 

 are on the same stage of development as the others, though the lamellae are somewhat shorter. 

 Another radial canal in the same specimen is bifurcated distally. The folded gonadial part has nearly 

 the normal shape, but the distal end of this part gives rise to two narrow, divergent canals, running 

 to the circular vessel. One of the lateral branches of this gonadial system is twice dichotomically branched. 



It has been acknowledged long ago, that the difference between Ptychogena lactea Agassiz and 

 Ptychogcna pinnulata Haeckel depends on development and variation. H a eckel's description is based 

 on two specimens from the Atlantic north of Rockall and a fragment of a specimen, found by the 

 "Challenger" expedition in the neighbourhood of Halifax. The two first mentioned specimens are in the 

 Zoological Museum of Copenhagen; thus I have been able to examine these specimens. Haeckel 

 states that the abaxial side of the tentacular bulbs is concave, whereas the adaxial side is convex, 

 and he gives a drawing in accordance herewith (Haeckel 1881, Plate II, fig. 4). Actually the fact is 

 the contrary (see Plate III, fig. 6). Moreover the cordyli have been drawn too large, especially too thick; 

 they are fairly thin in this specimen. There is another specimen from the same locality, very badly 

 preserved. As the specimen has hitherto been labelled " Thaumantias", and as Haeckel only mentions 

 two specimens from this locality, this specimen has, I think, not been in the hands of Haeckel. 



Bigelow's record of Ptychogena lactea from the north-western Pacific (1913) is of considerable 

 interest, partly owing to the statement of the occurrence of this species in the Pacific, partly on account 

 of the observation, that the young specimens have a comparatively larger number of cordyli than the 

 full-grown individuals; a specimen with about 50 tentacles had about 160 cordyli. 



Among other species, which have been referred to the genus Ptychogena, I have already men- 

 tioned (p. 1314) ''Ptychogena erythrogonotf Bigelow and "Ptychogena Hertwigi" Vanhoffen, which both 

 belong to the genus Chromatonema. 



The medusa, described by Maas (1893) as Ptychogena longigona from the north-eastern Atlantic, 

 has not been found since it was described by Maas, though numerous collections have been made in 

 the same region. Setting aside that ocelli are not mentioned in the description, this reminds one to a 

 considerable degree of Laodicea undulata, and I am, in fact, very much inclined to think that this is 

 actually the species described by Maas. 



Torrey (1909, p. 13) describes a species from San Diego, California: Ptychogena californtca. 

 Two young specimens were found, 10 mm in diameter by more than half as high, with about 48 tent- 

 acles, i 5 cordyli between every successive pair of tentacles, gonads with 12 14 folds. This is 

 undoubtedly a Ptychogena, but I dare not decide, whether it is a distinct species or only young 



individuals of Ptychogena lactea. 



5' 



