52 Bulletin American Museum of Natural History [Vol. XLII 



Only the life history of the holarctic species, fuscipes, has been 

 worked out but many authors have written about it. Cussac, 1855, 

 gave the first account of the egg-case and Schiodte, 1862, added the re- 

 maining stages. Miall, 1895, contributed an interesting account of its 

 biology but Balfour-Browne, 1910, must be credited with the most com- 

 prehensive treatise on the species. As yet, a complete description of the 

 pupa has not been presented. 



The egg-cases of both species are the first of the family to be ob- 

 served in the spring. The earliest record was April 16 for H. fuscipes. 

 The egg-laying continues in full force until the cases of Tropisternus 

 and various others begin to appear. Then a diminishing in the number 

 of cases takes place. However, the cases may be taken all through the 

 summer and the middle of August brings the greatest number again. 

 This latter statement is practically true of globosus also. The cases of 

 fuscipes are more frequently found away from the bank, attached to 

 floating vegetation, while those of globosus are placed in moss or in mud 

 at the shore-line and usually entirely concealed, except the cap end. 



Hydrobius globosus Say 

 Plate XI 



In contrast with fuscipes, H. globosus is uniformly abundant through- 

 out the entire summer. Adults gathered in the spring were placed in an 

 aquarium-terrarium. On April 16 several cases were observed buried 

 in the mud away from the water-line and only the cap and flare were 

 showing. To the casual observer this white silk would resemble mould. 



The next day one of the specimens was seen working on an uncom- 

 pleted egg-case. The cap had not been made and there were only nine 

 or ten eggs within it. Upon being disturbed, the beetle stopped spin- 

 ning but almost immediately recommenced. More eggs were being laid 

 and this process was interrupted only when the beetle wished to apply 

 the inner loose covering of silk. This process of adding the full comple- 

 ment of eggs required about half an hour and another half-hour was spent 

 in sealing up the opening. It took over an hour to make the broad flare 

 and nearly an additional hour adding silk here and there, apparently 

 making sure the case was properly sealed. Not only did it complete this 

 one case but another smaller case was soon formed next to it and the 

 flares of both fastened together. 



The number of eggs varies from thirteen to twenty-five but the 

 average number is twenty. The young larvae come out the cap end, 

 breaking through rather than pushing off the cap. No attempt was made 



