238 Mr. R. I. Pocock on 



minusque scaber, et granula in superficie superiore manuum 

 ejus majora sunt, humilia et rotundata, cephalothorax multo 

 brevior quam segmenta caudse l m + 2 m , cauda circiter 4J 

 longior quam cephalothorax, vesica latior quam segm. cauda? 

 5 m , parum longior quam latior, aculei longitudo vesica? lati- 

 tudine minor." 



However, in specimens of Swammerdami the colour of the 

 trunk varies from reddish brown to dark green ; the degree of 

 granulation also varies considerably, in smaller specimens the 

 granules upon the hands are relatively coarser and much more 

 defined than in larger specimens, in which they appear to 

 have been worn away and fused together ; the length of the 

 tail increases with the size of specimens and varies with sex, 

 being considerably longer in the adult male than in the adult 

 female. In young specimens the cephalothorax equals in 

 length the length of the first two caudal segments taken 

 together; in the adult female it is shorter and in the adult 

 male very much shorter ; the width of the vesicle also increases 

 with age; in small specimens it is as wide as the fifth caudal 

 segment, in large specimens it is much wider. 



So far, then, the differences between asper and Swammer- 

 dami may be accounted for on the supposition that asper is 

 merely an immature specimen. But on glancing over the 

 table of measurements given by Dr. Thorell of his type, 

 there may be noticed some curious facts which seem at first 

 irreconcilable with the view of the specific identity between 

 Swammerdami and asper. The following measurements are 

 given in millimetres : — Total length 97, cephalothorax 15|, 

 tail 60, first two caudal segments 16|, fifth caudal 13, width 

 of vesicle 5; manus, length 15^, width 12£. 



Now, if the accompanying table of measurements be exam- 

 ined, it will at once be seen that specimen N is almost of the 

 same length as the type of asper, and therefore, unless the 

 two be different species, the other measurements should 

 coincide approximately. But this is certainly not the case, 

 the measurements of asper being enormously greater in each 

 instance. But no doubt the explanation of this discrepancy 

 is that the type of asper being dry, the segments of the abdo- 

 men, as is often the case, have become drawn together by 

 the shrinking of the arthrodial membrane, so that the first 

 overlaps the second, the second the third, and so on. Now 

 specimen N is preserved in spirit and the tergites and sternites 

 of the abdomen are perfectly distinct. But if it be allowed 

 that the shrinkage in the type of asper amounts to a little 

 more than 2 millimetres for each abdominal segment, we may 

 roughly put the original length of the specimen at about 115 



