68 INVERTEBRATE ANIMALS. 



of the Arctic Seas. On the coast of Boothia they form 

 the food of prodigious shoals of salmon : in the Green- 

 land Seas two species form part of the food of the 

 common whale. Mysis Oheron, found on the coast of 

 Cornwall, is so transparent that in a tumbler of water 

 nothing of it can readily be seen but its pair of black 

 eyes. The Squilla, or Mantis-shrimp, so called from 

 its resemblance to an Orthopterous insect, exhibits most 

 of the body segments with their appendages perhaps 

 better than any other Crustacean. The larger species 

 are tropical, and it is probable that the animal, like the 

 Mantis, waits the approach of its prey within the reach 

 of its truly formidable fore-legs. Estimated number of 

 species : recent, 50 (M. Edwards) ; British, 18. 



Order DECAPODA. Uku, ten ; irovg, a foot. Gills 

 contained in cavities at the sides of the carapace. Pairs 

 of feet, five, the first pair at least chelate, i.e., termi- 

 nated by nipping claws. Includes Shrimps, Prawns, 

 Lobsters, and Crabs. 



3Iany of the finest examples in the series were obtained from 

 W. Hakpek Pease, hy whom they were collected in the Pacific. 



Tribe MACKOURA. [J-axpos, long; ovpoc, a tail. 

 That which is commonly called the tail is in reality 

 made up of segments of the abdomen, which in the 

 present tribe is terminated by a fan-shaped swimming 

 appendage or fin, obviously acting to the greatest advan- 

 tage when, by its powerful down-stroke, it propels the 

 animal backwards. 



Group 167.— Family PAL^MONID^. Prawns, Palamon, 

 differ from Shrimps in the position of the segments 

 bearing the antennae, and in the carapace, which in 



