CJIABS AND SPIDERS. 9 



in great bodies, and make their way by the shortest course to 

 the sea in order to deposit their eggs in its waters. When this 

 object is accomplished, they return in a weakened condition to 

 their burrows. Whether the CEningian species had similar 

 habits it is hard to say. At the CEningian epoch the sea had 

 disappeared from these regions ; but perhaps salt marshes and 

 small basins of salt water may have remained here and there, 

 which these crabs may have taken advantage of for the deposi- 

 tion of their eggs. The Swiss land-crab (Gecarcinus punctatus, 

 Heer) is rare at CEningen; the river-crab is more common. 

 Of the latter Prof. Heer has obtained twenty-eight, and of the 

 former only eleven specimens. 



b. Arachnida. 



CEningen alone furnishes information with respect to the 

 Spiders of the Swiss Miocene, these soft animals being preserved 

 only in the fine calcareous marl of the lower CEningian quarry. 

 From the upper quarry only two much- mutilated specimens have 

 been received. 



The Spiders hitherto found at CEningen belong to twenty- 

 eight species ; but their generic determination is very difficult, 

 as the principal characters, which depend upon the position of 

 the eyes, are not recognizable. Prof. Heer has endeavoured to 

 determine them by the general form of the body and the com- 

 parative length of the legs; and in accordance with these 

 characters they may be referred to ten genera. Figs. 211-221 

 represent the principal forms of the CEningian spiders. We 

 observe among them a cross-spider (Epe'ira molassica, Heer, 

 fig. 221) of the size of the Swiss common species; several crab 

 spiders (Thomisus ceninyensis*, T. Iwidus, and T. Sulzeri, figs. 

 215-217), which run sideways like crabs, and are distinguished 

 by the shortness of the two hinder pair of legs ; some weaving 

 spiders (Theridion annulipcs, fig. 212, and T. globulus, fig. 220), 



* Thorell refers this Thomisus to Xysticus and TJieridion maetdipes to Asa- 

 yena. But, according to Koch, Xysticus must not be separated from Thomi- 

 sus ; and, according to Walckenaer, Asagena is to be united with Theridion. 

 Considering the bad state of preservation of the fossil Arachnida, they can 

 only be referred to the most important genera. 



