166 



ridge of the iniddle valve may he yellow. Dautzenhergi is deeper 

 purple, with dark purple spots and stripes. Even a dark blue 

 colour with white and purple stripes and spots does occur. 



For the angle of divergence I found 110° for rissoi and daut- 

 zenhergi^ 105° for meneghini. 



As to the radula, I confirm what was mentioned by Thiele (71, 

 Pag. 285). This author writes: sWenugleich die als Chiton mene- 

 ghini beschriebene Form auf den ersten Bliek durch ihre starke 

 Radialskulptur sehr von den Exemplaren, die nur unregelmassige 

 koncentrische Furchen auf den Seitenfeldern zeigen, verschieden, 

 wohl auch meistens breiter ist, verhalt sich doch die Radula so 

 ahnlich, dass man wohl beide Formen nur als Unterarten unter- 

 scheiden wird." This I can confirm. 1 isolated the radula of the 

 three forms, but could not find any important diiïerence betweeu 

 them. 



When we consider all these data, we must conclude, that there 

 does not exist any well-marked diiïerence between Ischnoehiton 

 rissoi, meneghini and dautzenhergi. All transitions between them 

 are extant; all three forms live in the same places and by col- 

 lectiug a great number of specimens it will be possible to obtain 

 all the transition-forms. So I do not agree with Ancey's opinion, 

 who is certain, that dautzenhergi will be considered as a distinct 

 species. As to the form fragilis, of which Pilsbry writes: »smaller 

 in size, the sculpture obsolete, without tracé of radiating striae", 

 I cannot form any opinion, because I never saw a specimen of 

 this form. 



V. Ou the geographical distributiou of the Chitons. 



Eleven years ago Simroth gave in his »Mollusca" (Bronn's 

 Klassen und Ordnuugen des Thier-reiches, Abt. I, 1892 — 1894, 

 Pag. 307 , 350) an article on this subject. Since that time 

 however the number of species has so greatly increased, that I 

 will give a new list based on the geographical distribution. On com- 



