354 



DISCOVERY REPORTS 



already in the list above. Measurements of the bell, central disc and pedalia are given 



in Table II. 



Table II 



Showing measurements in mm. of the twenty-iiine specimens of 

 Periphylla hyadnthma. forma regina 



Size. Most specimens are from 100 up to 150 mm. in diameter. A single specimen 

 from St. 461 E has a diameter of 200 mm. The central disc is relatively broad ; the re- 

 lation betw^een height and diameter is very variable, but most specimens are rather 

 flatter than high. 



Form. Mayer called attention to the fact that the form of the bell apparently changes 

 with age, becoming flatter and relatively wider as the medusa grows larger (1906, 

 p. 1 137). I agree with this so far as the older stages are concerned, but not with respect 

 to the small " Bigelow" stages and stages of dodecabostrycha typica, which are generally 

 much flatter than the older transitional and hyacinthina stages. 



The SURFACE OF THE EXUMBRELLA is mostly perfectly smooth, though some specimens 

 show a radial structure of nettle-warts (St. 86) or a network of wide meshes (St. 383), or 



