ARKIV FÖR ZOOLOGI. BAND 3. N:0 11, 



Table of measurements and proportions in Fossil 

 and Recent species. 



Limulus priscus, Triassic I 12.5 



Limulus Walchi, Jurassic, a young in- i 

 dividual | 15.5 



Limulus Walchi, adult 72.5 



Limulus Decheni, Tertiary 1155 



Limulus Decheni, a very large individual j275 



Limulus polyphem,us, Recent, a large | 

 individual |210 



Limulus moluccanus, Recent 105 



49 7" 



46 7o 



42 7" 



51 7o 



In the above table are included all the fossil species of 

 Limulus excepting L. maximus and L. Nathorsti, for which 

 data for measurements are not available. The measurements 

 are expressed in millimeters. Those for the cephalothorax 

 are made following the curve of the test, but the length is 

 in a straight line. My own measurements are much fuller; 

 but enough is given here to indicate the size of the several 

 specimens. The ratios are of considerable interest as they 

 include practically all the known species. 



The ratio of the length to the width of the cephalothorax 

 is strikingly constant, not varying more than six per cent. 

 This is less variation than one would expect to find in the 

 individuals of a single species. The ratio of the length of 

 the abdomen to the length of the cephalothorax is more va- 

 riable, being markedly different in Limulus priscus. The 

 ratio of the length of the telson to the length of the whole 

 animal is again very constant. It is to be noted however 

 that we only know the length of the telson in one fossil 

 species. In Limulus decheni the telson is stout and from its 



