COLLEMBOLA OF MINNESOTA 31 



There is but one specimen of the third species in the 

 collection and I do not feel safe in giving it a name. It 

 is certainly distinct from both of the others but may pos- 

 sibly be a variety of some known species. 



Genus Isotoma Bourlet 1839. 



This genus is represented in our fauna by at least 11 species 

 and it is likely that more may be found. 



The body is cylindrical, sometimes a little flattened dorso- 

 ventrally. 



In color we may expect anything from pure white or black 

 or modest gray, to gorgeous greens and purples. The species 

 are all pretty active, especially those in which the legs and fur- 

 cula are long. The four-jointed antennae are rather short and 

 stout, often little longer than the head. In most species there are 

 sixteen ocelli present, but some cases of atrophy are found in 

 which the number on each side is reduced to seven, two, or 

 none. A postantennal organ, consisting of a more or less elon- 

 gate ring just caudad to the base of each antenna of found in 

 most species, and is often of importance in species determin- 

 ation. The feet bear two claws which are furnished with teeth 

 in many cases, and the tips of the tibiae are often provided with 

 one or several clavate hairs. The abdominal segments are sub- 

 equal in length. The furcula is usually fastened to the fifth, 

 though in a few of the lower species it seems to be shifting for- 

 ward so that it seems to proceed from the fourth segment as in 

 the Poduridffi. It seems to me probable that in all of the Iso- 

 tomas at least, the furcula really belongs to the fifth segment. 

 Perhaps further embryological studies will determine this for 

 certain, both in this genus and also in the Poduridae. The ventral 

 tube is w^ell developed, and quite prominent. 



We are especially fortunate in having the American spec- 

 ies of this genus written up by our best authority upon the sub- 

 ject, Mr. Alex. D. MacGillivray. In vol. XXIII of The Can- 

 adian Entomologist may be found his key to the more than 

 thirty species then known to be found in the United States. He 

 says "No measurements are given, as they have been looked up- 

 on as worthless ; the formulae of the claws and mucro are all that 

 are necessary to recognize the species, young or adults." 



