North African Specimens o/Apus ctuicrlForniis. 409 



dcpeiuls largely on the degree of contraction of the abdomen. 

 While the ventral spines of the Seottisli specimens are 

 always rather long and pointed, they are short and broad in 

 those from Tunis, ])ut still project beyond the segment. 

 In the 'rilghemt examples these spines are short and squaini- 

 form as in A. inaiiritanicus. 



Fiu-. 1. 



Posterior margin of shell, seen from the side. A, Spscimeu from Tunis ; B (more magnified), 

 from Scotland: tZo., dorsal carina^ showing teeth. C. Another specimen from Scot- 

 land, showing toothed carina. 



(3) The form of the telson in A. cancriformis and also in 

 Ghigi's new species is very constant, but there are differences 

 in the number and arrangement of the spines thereon. In 

 A. mauritanicus the only difference from the type apparently 

 consists in this — that the two lateral spines over the insertion 

 of the f ureal rami are of unequal size, the lower one being 



