360 



DISCOVERY REPORTS 



greatest depth (1500 m.) Broch found twelve individuals oi hyacinthina, in 500 600 m., 

 however, thirty-six. The maximum occurrence is in this layer. In 700-800 m. there are 

 nineteen, in looo-iioo m. eighteen specimens, in 1250 m. only seven and in 1500 m. 

 twelve specimens. The number diminishes rather from the stratum of 500-600 m. to 

 greater depths and the occurrence is not at all a regular one. 



Broch's table on p. 8, illustrating the vertical distribution of P. hyadnthina in the 

 "secondary centre" of the Sognefjord, is not in accordance with his statements either. 

 Here two maxima are present, one at 500 m. with 426 specimens, another in 750 m. 



Fig. 2. Chart showing the distribution of Periphylla hyadnthina, Steenstrup, 

 in the South Atlantic and Southern oceans. 



with 400 individuals, separated by the stratum of 650 m. with 72 specimens only. The 

 upper strata show no increase in the numbers of specimens either. Broch's table on 

 p. 9 on regina demonstrates nothing in this respect, the figures being too scanty. 



My Table III also shows that an increase in number with depth does not exist. The 

 numbers show a maximum occurrence for each stage, which lies for dodecabostrycha and 

 hyadnthina at 750-1000 m. and for regina at 1 250-1 500 m. It is possible that an 

 increase takes place towards these optima from the surface, in deeper layers a decrease 

 of numbers may take place (see forma regina). An interesting difference between Broch's 

 and my material is, that the maximum occurrence of the Michael Sars specimens of 

 hyadnthina is found in 500-600 m., but that of the Discovery specimens in 750-1000 m. 

 As to regina my results agree in general with those of Broch. 



