184 



it does not differ at all in the female in superficial characters, every 

 effort having failed to discover any feature whereby specimens of this 

 sex might be distinguished from each other. As the genital structure 

 is so distinct this is rather surprising, and the distinguishing feature 

 will no doubt be still discovered. 



The primary characters of the female genitalia are of the same type 

 shown in dtibia, but the distinction is yei obvious. The pubic process, 



while divided at tip much 

 as in the i^recediug species, 

 is only about half as long, 

 and does not divide the 

 upper plates as in the pre- 

 ceding species. It resem- 

 bles the upper part of the 

 duhia structure set upon 

 the superior plates ; these 

 latter are large and nearly 

 quadrate, In marked con- 

 trast with the narrow, 

 linear structures of duhia. 

 The inferior plates differ as 

 markedly, as can be readily 

 seen by a comparison of 

 the figures. 



The males also offer no 

 habital or other difterences 

 from duhia J except in the 

 ventral characters, but these are obvious and easily recognized. The 

 ridge in this species is very much curved, verj- much overhanging, the 

 ends reaching the apical margin of the segment, while the arch, com- 

 bined with the depression of the last segment, forms a perfect oval. 

 In this species the space included by the arch of the ridge is smooth; 

 in duhia it is punctured. 



This species seems rather more southern than the preceding. It is 

 practically the only form taken at Washington, many thousands being 

 taken while only one specimen of the other forms was discovered. 

 Other localities are New York, New Jersey, Central Missouri, Iowa, 

 Georgia. The specimens from New York and New Jersey are from my 

 collection, and form the small minority of the specimens taken. The 

 specimens from Central Missouri are from Professor Kiley^s collection, 

 and the figures in the Missouri Reports, so extensively copied, probably 

 represent this species. 



Finally, these forms represent a series of species, evidently derived 

 from the same stock, and which have differentiated in physiological 

 rather than superficial or habital characters. The^^ have become dif- 



FiG. 43.— Lachnosterna arcuata. 1, clasper of male from 

 front and above; 2, clasper of male (right) from side; 3, 

 clasper of male (left) from side ; 4, ventral characters of 

 male ; 5, genital structure of female ; 5a. puLic process ; 

 56, superior plates ; 5c, inferior plates — enlarged (original). 



^ 



