154 Papers from the Marine Biological Laboratory at Tortugas. 



In Polyclonia, on the other hand, it is impossible for the disk to assume 

 any such shape as that just described for the other genus. There is no 

 raised ring, no concave center, no mucous tissue. The top of the disk is 

 quite flat and smooth. 



Color pattern of Polyclonia. Instead of the circle of 12 to 20 rounded 

 spots which mark the inner portion of the disk in Cassiopea, we find that 

 in Polyclonia the dark coloration of the center extends in eight broad rays 

 nearly to the margin, and the spaces between the rays are evenly yellowish 

 in hue. Close to the edge of the disk are many oval or round white spots, 

 of small size and regular arrangement, one large one opposite each of the 

 sense-organs, smaller ones distributed between them. This part of the sur- 

 face in Cassiopea is, as has been indicated, entirely free from color markings. 



Marginal sculpturings. Whereas the margin of the disk is smooth in 

 the case of Polyclonia, a characteristic arrangement of radial grooves, extend- 

 ing various short distances in from the edge, is noticeable in the other 

 form under consideration. 



Marginal sense-organs. The marginal sense-organs in the two genera 

 show a difference in number. The specimen of Polyclonia which was ex- 

 amined, measuring 76 mm. in diameter, bore 12 sense-organs, while in an 

 average specimen of Cassiopea of this same size the number is 18. Even 

 in the smallest specimens, less than one-third as large as the example of 

 Polyclonia, 13 was the smallest number noted, and very many counts were 

 made. 



CASSIOPEAS FROM DIFFERENT LOCALITIES. 



The writer has had the privilege of examining specimens of this genus 

 from Jamaica, and has studied the characteristics of the specimens found 

 in the Bahama Islands and at the Tortugas. In the first and last-men- 

 tioned localities the conditions were much the same, but in the Bahamas 

 there was much less protection afforded the waters in which the medusae 

 were found. There was less of peculiarity in all the surroundings, the 

 temperature of the water, storm influence, and food supply being normal 

 for the shores of coral islands. The only points of difference to be noted 

 in the medusae are with reference to size and color-pattern. The average 

 size of the Bahama specimens taken at the same time in the summer was 

 considerably smaller than in the case of the others, and, while the mark- 

 ings, described by Bigelow as caused by the presence of zoanthellse in the 

 cells, were of the same general character, the spots and bands were less 

 sharply marked. 



The appended table gives the main features of the two species, Cassiopea 

 xamachana and Polyclonia frondosa. 



