THE CANADIAN ENTOMOLOGIST. 47 



THE AMERICAN SPECIES OF ISOTOMA. 



BY ALEX. D. MACGILLIVRAY, ITHACA, N. Y. 



The genus Isoio/na, as far as known, is confined to the Northern 

 Hemisphere and to the more northern part of this region. Thirty-one 

 species are recorded from Europe and Asia, while the same number is 

 recorded in the present paper^ from the Eastern United States. 



The characters for differentiating the species of Isotoma are all drawn 

 from the form of the claws and the apical segment of the spring. In the 

 following descriptions, the larger claw is referred to as the superior and 

 the smaller as the inferior claw. Several species have the superior claw 

 trilobed when viewed from above; the lateral lobes appear as a large tooth 

 along the outer margin of the claw when viewed from the side. The 

 tarsi consist of a single segment. The apices of the tibiae in many 

 species bear long, club-shaped hairs, which are known as tenant hairs. 

 The spring is known technically as the furcula, its basal segment as the 

 manubrium, the middle segment as the dentes, and the apical segment as 

 the mucro. In the following descriptions, the furcula is considered as if 

 extended caudad, the toothed edge being dorsad. The horizontal teeth 

 of the mucro are those having their axis parallel to the axis of the mucro, 

 and the vertical teeth those in which their axis is perpendicular to the 

 axis of the mucro. The teeth are numbered from the apex cephalad. 

 No measurements are given, as they have been looked upon as worthless; 

 the formulae of the claws and mucro are all that are necessary to recognize 

 the species, young or adults. 



I am under obligations to Mr. Samuel Henshaw, Museum Compara- 

 tive Zoology, Cambridge, Massachusetts, for an opportunity to study 

 the types of Dr. Packard, including all his species except Besselsii and 

 Walker a ; to Mr. L. O. Howard, Department of Agriculture, Washington, 

 D. C, for type specimens of Besselsii a.\\d of pahisiris, MuUer, from 

 Sweden, determined by Dr. Tycho Tullberg ; to Mr. Nathan Banks, Sea 

 Cliff, N. Y., and many others, who have been given due credit for the 

 presentation of specimens. 



1. Superior claw without teeth on the inner margin 2. 



Superior claw with teeth on the inner margin ; 18. 



2. Mucro with the first tooth at the base of the second 3. 



Mucro with the first tooth not at the base of the second 8. 



3. Inferior claw with a tooth on the inner margin ; superior claw without 



teeth on the outer or inner margins ; tibire without tenant hairs; 



