ENTOMOSTRACA OF MINNESOTA. 55 



The American literature has been unfortunate in respect to this 

 genus, chiefly because the European species were so imperfectly de- 

 scribed that satisfactory differentiation was impossible. Within the 

 last few years this difficulty has been removed, and the work of 

 DeGuerne and Richard has laid the foundation for careful discrimina- 

 tion. It is thought advisable to reproduce the essentials of the de- 

 scriptions of the known species so that other students may have the 

 means of identifying our species, only a small part of which are as 

 yet satisfactorily known. 



KEY TO THE GENUS DIAPTOMUS. 



I. Male with a hooked appendage on the last joint of the right anten- 

 na asiaticus, 56; denticornis, 56. 



II. Male with a serrated plate on the antepenult segment of the right 



antenna. . . scrricoiii.s, 56; wierzejj»kii, 57; pectinicornis, 57; 



tryboiiii, 57; hircus, 57. 



III. Male with the appendage of the antepenult segment of the antenna 



prolonged into a curved hook longer than the penultimate seg- 

 ment eiseni, 58; fraiiciscanus, 58. 



IV. Male with the appendage of the antepenultimate joint of the an- 



tenna straight, and as long as or longer than the penultimate 

 joint. 



a. The basal joint of the right foot of the fifth pair in the male with 



an external accessory process salinu^, 59; laticep.s, 59. 



b. The basal joint of the right male fifth foot without a proce.'S. . iiiinutus, 59; 



aslilaudi, 60; sicilis, 60; baccillifer, 61 ; slioshone, 61. 

 V. Male with the appendage of the antepenultimate joint of the an- 

 tenna shorter than the penultimate joint. 



a. The first segment of the abdomen unsymmetrical, with a strong 



process upon the right side. . sig-nioaiidatiis, 63; incongriiens, 63; 



gibber, 63. 



b. The antepenultimate segment of the antenna of the male with a 



hyaline appendage along its outer margin. 



* Inner ramus of the right fifth foot of the male shorter than the 



basal segment of the external ramus. . zacharia.si, 64; leptopus, 64. 

 ** Inner ramus of the right fifth foot of the male longer than the 



basal segment of the outer ramus. . . tatricilS, 65; coeriileilS, 65. 

 e. The antepenultimate segment of the right antenna of the male 

 without a straight lamina. 



* The process of that segment very short and obtuse. . . . gracilis, 66. 

 *'' The process of the antepenultimate segment of the right male 



antenna long and pointed. 

 t Inner ramus of the left fifth foot of the male shorter than or 



nearly equal to the basal joint of the outer ramus. . orientalis, 66; 

 stag-nalis, 66; albuquerquensis, 67; lintoul, 68. 

 tt Inner ramus of the left fifth foot longer than the basal joint of 



the outer ramus .siciloide.s, 69; novaniexicaiius, 70; 



sanguineus, 71; niinnetonka, 71; arniatus, '32. 



