92 Transactions. — Zoology. 



Idoteidcz and approaches the Tanaidce. The legs consist of an anterior 

 series of four, and a posterior series of three, and this, according to the 

 figures given by Bate and Westwood, appears to be the case with the 

 TanaidcB. This peculiarity is also possessed by the Amphipoda to which 

 Phreatoicus has a considerable superficial resemblance due chiefly to the 

 flattened form of the body, best seen in the abdomen, and to the fact 

 that the segments of the pleon have the integument produced downwards, 

 but also to the Amphipodan facies of the legs and the last pair of pleo- 

 poda. 



The precise place of Phreatoicus in any system of classification cannot 

 as yet be indicated with certainty, but one thing is made clear by the dis- 

 cussion, viz., that Phreatoicus, possessing as- it does affinities to several dis- 

 tinct groups, must be of very considerable antiquity. 



The occurrence of this species has been somewhat remarkable. Ever 

 since January, 1881, I have collected or had collected for me all the 

 Crustacea that were observed to come up ; nothing new was found until 

 the beginning of September, 1882, when a single specimen of Phreatoicus 

 was obtained, and in the short time since then six other specimens have 

 been found. 



DESCRIPTION OF PLATE IV. 

 Phreatoicus typicus. 

 Fig. 1. Lateral view of trie animal x 5. 



2. Upper antenna X 30 ; a, auditory cilium from the same, more highly magnified. 



3. Base of lower antenna X 13. 



■4. Side view of the head, showing the mouth organs in position, X 15 ; a, labrum ; 

 b, mandible with appendage ; c, the two lobes of first maxilla ; d, second max- 

 illa ; e, maxillipede with/, the rounded plate at its base. 



5. Mandible, view of inner side X 30. 



6. Labrum X 30. 



7. First maxilla X 30. 



8. Second maxilla x 30 ; a, seta rom middle lobe of same, more highly magnified 



9. Maxillipede X 30. 



10. Distal portion of first thoracic leg X 30. 



11. Seventh thoracic leg X 13 ; a, end of same X 30. 



12. First pair of pleopoda X 13. 



13. Second pair of pleopoda X 15. 



14. Extremity of abdomen, side view, X 14. 



15. Portion of the integument X 120. 



