39 



chance the mantle of the animal in the Auodonta of fig. 1 had been sa- 

 ved, and we see that in this mantle the impression of the crest appears 

 clearly (see fig. 2. The < — indicates the direction where the water 

 streams in and on the edge of the mantle we see the papillae which are 

 around the entrance.). The impression in the mantle exactly follows 

 the bends of the crest, as is clearly to be seen if we compare fig. 1 with 

 fig. 2. The impression of the mantle fitted on all sides very closely 

 round the crest — . 



I have once observed a case in which, on a natural regenerate, 

 2 crests and a few little pearls were found on the newly formed mother- 

 of-pearl. According toKubbel crests are already to be recognized on 

 the outside of the shells , but in my opinion this is not nearly always 

 the case. In the big crest described above, for instance. 



Rubbel says that in Anodonta ceUensis "Schalenconcretionen 

 überaus häufig vorkommen". I found among 614 specimens of Ano- 

 donta cijgnea and Anodonta ventricosa^ only 5 specimens with crests. 



Fig. 2. ^1. cycjnea. Mantle. 4/5. 



And among as many specimens, I found 6 natural regenerates, so I 

 could at the utmost mention 11 ''concretionen" among 614 shells; I 

 cannot call this a great number. Rub bel also finds very few pearls 

 in An. cell, though he examined some hundreds of shells. In my opinion 

 pearls are decidedly found much more generally in A. cygnea and A. 

 ventricosa. Besides an Anodonta I have also once found a little crest 

 on Dreissensiapolymorplia. Besides in this shell the top, apex, was filled 

 with a relatively very large concretion of very irregular form and while 

 grinding it, I found that this concretion was partly hollow partly massive, 

 and highly irregular. The massive part showed some nuclei of perio- 

 stracum around which all was filled up with layers of lime. I found no 

 trace of a parasite and on the outside the shell was quite sound. Fi- 

 nally I want to give a short description of a few other abnormal findings 

 in Anodonta shells. An A. cygnea showed a layer of brown periostra- 

 cum with a surface of 2 1/2 — 3 cm- on the ordinary mother-of-pearl 

 on the inside. Besides, above this spot, near the apex, again exactly 

 such a piece of periostracura, 3^2 cm long and 1/2 cm wide. These 

 2 secondary layers of periostracum are partly covered again with a thin 



