192 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



into 4 pairs of rhopalar, and 4 pairs of tentacular lappets. A deep 

 annular furrow separates the dome-like apex of the exumbrella 

 from marginal zone of bell. Between this ring-furrow and the 

 lappets is a zone of 16 pedalia, 12 in the tentacular and 4 in the 

 rhopalar radii, and these are separated one from another by 16 

 deep, radiating clefts which extend down the mid-axial lines of 

 the lappets. There are four deep, interradial sub genital pits in the 

 floor of the subumbrella, lined above their edges by rows of internal 

 gastric cirri. The large central stomach extends peripherally out- 

 ward into the subumbrella 

 in the four perradii. These 

 four openings lead into a 

 wide ring-sinus in the sub- 

 umbrella, which in turn 

 sends out a radiating vessel 

 in the radius of each tenta- 

 cle and rhopalium, 16 in all. 

 These vessels fork before 

 reaching the tentacles or 

 rhopalia, and their diverg- 

 ing ends curve around the 

 edges of the lappets and 

 form a marginal ring-canal. 

 I believe that Periphylla 

 hyacinthina can not be sep- 



Fig. 5. — Periphylla hyacinthina from the arated specifically from P. 

 Hawaiian Islands, showing range in slope J, O de C ab OStry cha. The 



OF THE BELL. * 



shape of the bell is quite 

 variable, and when large the medusa usually becomes relatively 

 flat and domelike, whereas it is relatively high and conical when 

 young. P. hyacinthina is said to be densely pigmented with pur- 

 ple-brown so that the gonads can not be seen through the bell 

 walls, whereas P. dodecabostrycha is said to be less densely colored 

 and semitranslucent. This distinction does not always apply, and 

 certainly the degree of pigmentation appears to be quite independ- 

 ent of the shape of the bell, whether flat and domelike or high and 

 pointed. Browne (1910), in his study of the Scyphomedusae of the 

 National Antarctic Expedition, concludes that P. dodecabostrycha 

 is probably only a large-growth phase of P. hyacinthina, and with 

 this opinion I am heartily in accord. 



