575 
Recht interessant wäre es, zu erfahren, ob der Herzog von Bedford 
noch mehr Penrice-Wasserböcke in Woburn Abbey besitzt, oder ob der 
bisher nicht erkannte Vertreter dieser Art, über welche die Literatur 
noch so merwiirdig arm ist, auch dort ein Unikum war und vielleicht 
mit onctuosus zusammen aus seiner Heimat im Siidwesten von Benguela 
dorthin gekommen war. | 
2. Regeneration of the shell of Unio and Anodonta. 
By A. B. van Deinse, Assistant, Zool. Lab. Leiden. Holland. 
(With 2 figures.) 
eingeg. 17. März 1912. 
Rubbel’s and Rassbach’s communications about experiments 
of regeneration of Anodonta and Margaritana, executed at Marburg in 
1910 and 1911 (Zool. Anz. Bd. 37, 1911, S. 169—172 and Bd. 39, 1912, 
S. 35—38) remind me of some observations I made three years ago. On 
the 17 of January 1909 I made an excursion in the environs of Utrecht 
and found three shells near Old-Amelisweerd Castle on the bank of the 
»Krommen Rijn« an almost stagnant river shut off by sluices. Two 
specimens of Anodonta and one of Unio. All three had the same pe- 
culiarity. The outside of the shells showed a big hole, about in the 
middle, and on the inside of the shell a large bubbly regenerate was 
clearly to be seen. The regenerate was perfect in the three cases and 
so the mussel had completely shut the hole. Remarkable was the great 
difference in surface between the hole on the outside and the regenerate 
on the inside of the shell (compare figs. 1 and 2). The surface of the 
regenerate is about 30 times as large as the surface of the hole. The 
regenerate is situated exactly between the impressions of the front and 
back adductor muscles and is squarish (see fig. 2). If one holds the shell 
against the light, the regenerate is outlined in black. 
This black colour is caused by the sand that penetrated into the 
shell through the hole on the outside. This stands to reason as the 
mussel lives on the bottom of the water. Proportional to the big rege- 
nerate was the quantity of the sand that had penetrated into the shell, 
and which weighed more than 1,5 gram. Besides sand, about ten bigger 
stones, a Planorbis, and two shells of Daphnia and Cypridina had pene- 
trated into the shell together with some parts of plants. The bubbly 
regenerate on the inside was covered with a layer of mother-of-pearl, 
running into the mother-of-pearl of the other part of the shell. Through 
the hole on the outside of the shell the regenerate at the outside is 
clearly to be seen after removal of the sand, and then the scaly perios- 
tracum is remarkable. I found all this in the three shells in the same 
