42 



MEDUSA. I. 



In the following I am going to present some scattered morphological observations, made on 

 the material of Staurophora mertensii from the North-Atlantic area, examined by me. 



The lower, free margin of the folded mouth-edge is sharply turned outwards as in Laodicca 

 and Ptychogena. 



In full-grown specimens the gonadial folds are more highly developed in the middle part of 

 the cross-arms than in the proximal and distal parts, each cross-arm thus being narrowly lancet- 

 shaped. The primary lateral folds have usually 4 — 6 secondary folds, more seldom 7 or more. In middle- 

 sized specimens the primary folds have, as a rule, the same number of secondary folds as in full-grown 

 specimens, but as the sexual products are not fully developed, and the walls accordingly are thinner, the 

 secondary folds do not come into contact, but are separated by open spaces. During growth of the animal, 

 new primary folds are formed intermediary between the existing ones. The lateral folds are flattened 



Table IV. Dimensions of some specimens of Staurophora mcrteusii 

 from Greenland and Iceland. 



calculated. 



on their upper (umbrellular) side, but they are only fastened to the subumbrella by narrow branched 

 lines (see Plate II, fig. 9, presenting some lateral folds seen from the aboral side after being carefully 

 loosened from the subumbrella). 



The largest breadth of the cross-arms and the length of the distal parts of the radial canals, 

 free of gonads (the "proper" radial canals) have been measured on some specimens from Greenland 

 and Iceland. The results are presented in Table IV, in which I have also given the number of tent- 

 acles. The numbers of localities will be found in the list of material below. The specimens are arranged 

 according to the size. 



In larger specimens the peripheral part of the exumbrella is provided with numerous deep, 

 sharp, radiating furrows of very different length, though rarely more than 10 mm long; the number 

 of furrows is variable, one being found off every second or fourth of the tentacles (see Plate I, fig. 9). 



The tentacles (Plate I, fig. 9; Plate II, fig. 10) are hollow. The basal bulbs are conical; the 

 ectoderm of the bulb is somewhat thickened, particularly on the adaxial side (Plate II, fig. 10). Every 



