Spiders of the Suh Family Lijssomance. 233 



eyes), measure from the anterior .edge of the eyes of the second row to the 

 posterior edge of tlie eyes of the f ourtli row. 



Wliere the expression ' ' width of tlie quadrangle of the eyes " is used, the 

 greatest width is always meant. 



The position of the eyes of the third row is determined by measuring 

 from the posterior edge of the eyes of the second, and the anterior edge of 

 the eyes of the fourth row. 



DISTRIBUTION OF THE LYSSOMA.NII. 



The distribution of the species of Lyssomanii presents some interesting 

 facts. The genus Asamonea falls very naturally into two divisions. The 

 two species constituting the first division, A. gracilis and A. flava, ai'e con- 

 fined to South America; the four species forming the second division are 

 restricted to Southern Asia and South Africa. At first sight it would seem 

 well to have formed two genera, allotting to each the Asemoneae of a 

 hemisphere. Careful study of the species, however, has convinced us that 

 such a proceeding would have been unadvisable, as the morphological char- 

 acteristics of either grouji could not be raised to generic importance. 



All ten species of Lyssomanes belonging to the sub-genus Jelskia are con- 

 fined to Central and South Ajnerica. The sub-genus Maroussa resembles 

 Asamonea in that its species are divided between two hemispheres. One 

 species only, M. modestus, is rejported from the old world, occurring in 

 Madagascar; of the remaining seven new world forms, five occur in South 

 America, one in the island of San Domingo and one in the southern states 

 of the Union. 



Regarded as an isolated fact, this distribution of the members of a genus 

 over the tropics of two hemispheres seems anomalous. But analogous 

 cases in the distribution of otiier oi'ganisms are by no means rare. Among 

 plants especially such cases are common. Among animals we may cite 

 the case mentioned by Wallace of the four species of Megacephala 

 (a genus of the CicindeUd^e, or tiger beetle family) two of which occur in 

 Africa and two in South America. In like manner four species of another 

 genus, Peridexia, of the same family, are equally divided between South 

 A. nerica and Madagascar. Then again when we consider the great anti- 

 quity of the existing genera of spiders, we can see nothing difficult of ex- 

 planation in the wide and discontinuous distribution of the Asamoneae and 

 Jlaroussae. We have only another instance confirmatory of the truth of 

 Wallace's remarks taat "' Insects exhibit in a very marked degree in their 

 actual distribution the influence both of vorj* ancient and very modern 

 conditions of the earth's surface. The effects of the ancient geographical 

 features of the earth are to be traced in the large number of cases of dis- 

 continuous and widely scattered groups which we meet with in almost 

 every family, and which, to some extent, obscure the broader features of 

 distribution due to the period during which the barriers which divide the 

 primary regions have continued to exist."* 



* A. R. Wallace, Distribution of Animals, Vol. I, p. ;503. 



