D. J. SCOURFIELD ON ILYOCRYPTUS AGILI8. 431 



of course it is only relatively so. In common with all the species 

 of the genus so far as known, it is a bottom-dwelling animal, and 

 practically incapable of swimming. It can, however, as I had 

 opportunity to observe, raise itself from the bottom and swim for 

 short distances. This is a feat altogether beyond the powers of 

 /. sordidus, except when very young, but Herrick says that his 

 /. spinifer can also swim until " loaded up with old clothes and 

 filth." As is very commonly the case with mud-loving Entomos- 

 traca, /. agilis is of a reddish colour, but the specimens I obtained 

 were not so red as I usually find /. sordidus. 



In conclusion, a few notes about the described species of 

 Ilyocryptus, while not pretending to be sufficient in all cases for 

 specific determination, will yet serve to indicate the relation of 

 /. agilis to its allies. 



/. sordidus, Lievin. — The first described and best-known form. 

 Moult incomplete. Posterior marginal set^e with several accessory 

 spines. Anus situated slightly posterior to middle of dorsal margin 

 of post-abdomen. Median (pre-anal) row of post-abdominal teeth 

 10-14, subequal. Length ^VVct"- 



/. acutifrons, Sars. — Moult complete. Posterior marginal setse 

 with one accessory spine. Anus near claws, a character which 

 separates this from all the other species. Median row of post- 

 abdominal teeth, about six, the anterior two nauch enlarged. 



Length ^V'-^V-'' 

 /. agilis, Kurz. — Moult complete. Posterior marginal setse 



with one accessory spine. Anus slightly anterior to middle of 

 post-abdomen. Median post-abdominal teeth, about eight, increas- 

 ing in size anteriorly. Length 4'o""?V"' 



The three foregoing species are European forms. 



/. spinijer, Herrick. — Only recorded from the United States. 

 Moult incomplete. Posterior marginal set^ with one accessory 

 spine. First antenna?, very long, rather more than eight times as 

 long as broad. Anus slightly anterior to middle of post-abdomen. 

 Median post-abdominal teeth, about ten. Outer row of elongated 

 post-anal spines only four or five in number. 



/. Halyi, Brady. — Described from specimens received from 

 Ceylon. Moult incomplete. No definite statement made as to 

 number of accessory spines on posterior marginal set^e. Anus 

 slightly anterior to middle of post-abdomen. Median po>t- 

 abdominal teeth, six or seven. Length ^'g". 



