Peracarida — Mysidacca, Cumacca. 



39 



There are Table-case 

 No. 5. 



The eyes, when present, are stalked and movable 

 swimming branches (exopodites) on the thoracic legs. 



Most of the Mysidacea live in the sea and many species are 

 found on the British coasts. Macromysis flexuosus is one of the 

 commonest species. A coloured drawing of the closely allied 

 Leptomysis is hung in Wall- case No. 5. A drawing of Arachno- 

 mysis leuckarti in the Table-case gives an example of the remark- 

 able forms assumed by some deep-sea members of the Order. The 

 family Lophocjastridac, all of which are inhabitants of the deep 

 sea, reach a much greater size than do the members of the other 

 families. A specimen of Gnathopliausia calcarata from the 

 " Challenger" expedition is exhibited, and alongside of it is placed 



Fig. 19. 



GnatJiopliausia willemocsii, female, from the side, one-half natural size. 

 gr., a groove dividing the last abdominal somite. (From Lankester's 



" Treatise on Zoology," after Sars.) 



a copy of a coloured drawing from a living specimen of G. ivil- 

 lemoesii (Fig. 19), showing the vivid red coloration characteristic 

 of many deep-sea Crustacea. 



Order 2. — Cumacea. 



A carapace is present, but it leaves four or five of the pos- 

 terior thoracic somites free. The eyes are not stalked, and are 

 usually coalesced into one. Swimming branches (exopodites) are 

 usually present on some of the thoracic limbs. The abdomen is 

 generally very slender, and the last pair of appendages (uropods) 

 are elongated. The other alidominal appendages are absent, at 

 least in the female. 



The Cumacea are all marine, burrowing in sand and mud, and 

 being occasionally taken in great numbers swimming at the 

 surface of inshore waters. As a rule, they are very small, the 

 specimens of the common British species IpJiuioi- trispinosa here 



