THE NAUTILUS. 33 



before, being subtriangular in outline, and having hooks. But 

 they are rather small, length and height being about equal, 

 0.21 rnm. This is entirely at variance with the statement of 

 Harms (Zool. Jahrb. Anat., 28, 1909, p. 332) and Haas (Pr. 

 Malacol. Soc. London, 9, 1910), quoted in my text, p. 275, that 

 they are 0.29 mm. long. But possibly this is simply a slip of 

 the pen or a misprint. 



UNIO TUMIDUS Eetzius. 



I have gravid specimens, received from W. Israel, collected 

 in Germany on May 22 and 27, 1911. One of the first date 

 had unripe glochidia. 



The structure of the soft parts is exactly like that of U. pic- 

 torum. The glochidia are immature, and the hooks are not 

 yet developed. In general shape they resemble much those of 

 U. pictorum, but they seem to be smaller, 0.19 mm. ; but this 

 should be confirmed by the measurements of ripe glochidia. 



UNIO CRASSUS Retzius. 



W. Israel sent me gravid females from Germany, collected 

 on May 2, 12, 25, 26, and on June 6 and July 21, 1911. Glo- 

 chidia were found in specimens collected on May 26 and June 

 6, on the latter date they were being discharged. In addition, 

 a single gravid female with eggs was collected on December 

 24, 1910, but this is regarded by W. Israel as an exceptional 

 case. Also the date July 21 appears as somewhat abnormal. 

 The normal breeding season apparently lasts from April to 

 June. 



Also here the structure is similar to that of U. pictorum. 

 Placentae distinct only, when eggs are present, and not very 

 solid. In the discharging female the glochidia were in the 

 suprabranchial canals in loose, irregular masses. Glochidia 

 of the same shape as in U. pictorum, but slightly smaller, and 

 less high in proportion to length ; length 0.19-0.20, height 0.18- 

 0.19. 



THE WATER CANALS IN THE MARSUPIUM OF THE ANODONTINAE. 



Lefevre and Curtis (Bull. Bur. Fisher, 30, 1912, p. 133) re- 

 gard the lateral or secondary water canals ("respiratory 



