136 Illinois State Laboratory of Natural History. 



without specific value. The following, taken from Herrick and 

 Turner '95a, p. 72, is his most complete description. "It 

 appears to be allied to sanguineus . The antennae are said to be 

 shorter than the body, the caudal stylets narrow, the right 

 male antenna has a hook upon its antepenultimate joint 

 and is strongly geniculate. But the one feature which may 

 determine the species is the existence of a tooth or spur near 

 the base of the claw of the right fifth foot of the male." 



In collections from Phelps Lake, Havana, 111., made May 

 18, 1894, occurred a single male specimen of a variant of D. 

 sanguineus which might easily be described as a new species 

 if the spine at the base of the terminal hook were taken as 

 the one specific characteristic to which all others must be 

 subordinated. This spine is straight and minutely dentate 

 on both margins. In all other respects, except a slight dif- 

 ference in the length of the terminal hook, the specimen is 

 a normal D. sanguineus. The fifth pair of legs is shown in 

 PI. XXV., Fig. 5. The occurrence of this specimen, taken in 

 connection with the loose descriptions of armatus, has led me 

 to believe in the identity of Herrick' s species and this variant. 



In regard to D. minnetonka, Marsh ('93) points out that 

 it is probably but a variety of D. sanguineus. In his "Synopsis 

 of the Entomostraca of Minnesota" Herrick says : "We are 

 inclined to agree with Marsh that this form is but one of the 

 many variations of 1>. sanguineus" ; but he nevertheless retains 

 minnetonka as a species name instead of making it a synonym 

 of sanguineus. 



Diaptomus sanguineus occurs in early spring in standing 

 water in connection with D. stagnalis Forbes, from which it 

 may be distinguished at a glance by the difference in size, 

 D. stagnalis being about twice as large as D. sanguineus. The 

 latter is generally a deep red, but D. stagnalis is often blue, 

 with abdomen and antennas a brilliant red. 



The theory of Herrick (Herrick and Turner, '95) in regard 

 to the transition of forms, "beginning with J >. stagnalis and 

 passing through several varieties to I), sanguineus later in 

 the season," will not hold owing to the fact that sexually 

 mature specimens of both species have been found in the 

 same pools at the same time. 



