165 



ghini^ I suppose, that the length of the two forms must be the sarae. 



About the number of gills nothing has been hitherto known. Ifound 



the following numbers for length, breadth, number of gills and slits. 



length breadth gills to the left and right slits T VIII 



rissoi 



9% 5 17-19 



The form dautzenhergi therefore is in genera! larger. 

 Por all the three forms the gill-row is of the adanal type. 



The girdle is covered with crowded, imbricated scales, In this 

 respect there exists a difference between the three forms. In fig. 

 10 A we see scales of rissoi; they show a number (9 — 16) of 

 well developed ribs, which converge to the outer margin. Those 

 of meneghini have con verging, but not uniting ribs (Fig. 11 A); 

 the outer margin on the contrary is denticulated. Those of daut- 

 zenhergi are either like those of rissoi or like those o( meneghini; 

 transitions between both forms of scales also occur. So there does 

 not exist a great difference in the covering of the girdle between 

 the three forms. The underside is covered with crowded calcareous 

 spines; the margin of the girdle has flat calcareous plates with 

 little grooves at the top. A comparison of the figures 10 B, C 

 and 11 B, C shows, that in this respect there does not exist any 

 difference. 



The colour is very variable. The valves of rissoi are light brown 

 or yellow, spotted and maculated with white, red and brown. 

 Constant is the blotching of the hinder margin of the valves 

 with red and white. The girdle is yellow or light brown. The 

 colour of meneghini is about the same as that of rissoi, but the 

 valves are ofteu purple and show irregular black spots, while the 



