40 



layer of lime with a great number of little pearls (?) on it, especially 

 along the edges. This layer of lime is so thin in many places that the 

 brown secondary periostracum shines through it. Of a parasite covered 

 up, as Rubbel (Zool. Anz. Vol 39 Nr. 21/22 S. 632—643) describes, 

 viz. a larva of an insect (long 2 cm) covered with "Schalensubstanz", 

 I found nothing here. The pearls (?) mentioned just now, beautiful, 

 exactly round grains, very finely striped radiantly, and with equally fine 

 concentric layers are lying both each separately and many melted to- 

 gether on the big brown piece of secondary periostracum. They rather 

 remind one of "the white grains of lime", which form the beginning of 

 the "polygonale Felderung", of the prismatic layer, however they are 

 rounder, much bigger and much sharper striped radiantly and concen- 

 trically. They are much thicker too and I found no reasons to take 

 them for these grains of lime of the "polygonale Felderung". Besides 

 there are in the shell 3 big crests and a great number of little pearls 

 grown to it. All these are developed especially on the obtuse side of the 

 shell. On the outside of the shell, not a single abnormality whatever, 

 is to be found. This is the finest example of succession of layers of 

 periostracum and lime, which I ever found in an Anodonta. Here we 

 have, going from the outside to the inside: periostracum (primary), pris- 

 matic layer, mother-of-pearl, another periostracum (secondary) and 

 another layer of mother-of-pearl with a great number of little pearls (?) 

 in it. And all this extends over a great part of the surface of the shell! 

 So, here, the mantle has successively given life to very different layers 

 indeed. I have not been able to find out what was the cause of this; 

 I found nothing of a parasitic influence as I said already before. To 

 this we can apply what Rassbach says (Zool. Anz. Bl. 38, Nr.l, Bd. 39 

 3. Jan. 1912): . . . "daß das gesamte Außenepithel des Mantels im- 

 stande ist, je nach Bedarf das Produkt der Sekretion zu ändern" . . . 

 In the impression of the adductor muscle on the obtuse side of a 

 shell of Anodonta rentricosa was found a concrescence of pearls, with 

 a surface of about 1/9 cm 2. The so-called "oil-stains", "Olfleckchen'", 

 are sometimes found also in Anodonta^ beautifully developed. I found 

 as many as twelve, mostly near the apex. Another Anodonta ventricosa 

 showed a burst on the outside. This burst has caused the origin of 

 some crests and some pearls, bubbly on a large brown spot on the inside 

 of the shell, exactly at the place of the burst. These were again near 

 the apex. The last case is an A. cygnea with, in the middle, a little 

 more near the top, 2 parallel dorsal crests, one of 1,5 cm and exactly 

 under it one of 31/2 cm. The uppermost has in the middle of its course 

 a thick pearl, of about 3 mm. Further some more very small pearls 

 are to be seen, scattered about. On the outside cf the shell no damage 



