166 LIFE BY THE SEASHORE. 



not infrequently in rock pools, especially at low tides. Such 

 specimens are usually females carrying eggs. The colour is 

 greyish white with touches of brighter colour. The differ- 

 ences from the preceding species are not very well marked, 

 especially if only small specimens of P. serratus are avail- 

 able ; but it will be noticed that in the present form the 

 rostrum is nearly straight, and has seven or eight teeth 

 above, and only three beneath. The rostrum is also rela- 

 tively shorter, and it does not usually exceed the length of 

 the antennal scale. The whole prawn does not exceed two 

 inches in length. Either of these prawns will repay careful 

 study, for which their relatively large size peculiarly fits 

 them. There are some other British species of Palcemon, 

 but these are rare, and need not be considered here. 



The next form to be considered is the Esop prawn, or 

 shrimp (Panddlus annulicornis), which, like the true prawns, 

 is typically an inhabitant of deep water, but is occasionally 

 met with in rock pools. It is of much the same size as 

 Palcemon squilla, which it resembles not a little, but is of 

 a somewhat brighter colour, the long antenna in particular 

 being in life beautifully ringed with scarlet. Like most of 

 the smaller Crustacea, it loses most of its beauty at death, 

 owing to the disappearance of the delicate transparency of 

 tint. In general shape and appearance the Esop prawn 

 resembles the true prawns, but can be distinguished from 

 them by the humped back, and by the different character of 

 the legs and antennules. In these respects it resembles the 

 next genus, Hippolyte, much more closely than Palcemon, 

 and the student should not fail to notice how closely the 

 three genera resemble one another, and how the Esop prawn 

 stands midway between the other two. 



As to the detailed characters of Pandalus, notice that the 

 hump-backed appearance is due to the fact that the third 

 abdominal segment is pouch-like, being much longer on 

 the upper than the lower surface, so that the tail cannot be 

 completely straightened. Further, the antennules bear two 

 filaments only instead of three as in Palcemon, and one of 

 these is thickened and curiously curved. Again, the first 

 pair of legs end in exceedingly minute chela?, and the 

 second are slender, thread-like, and of unequal size. The 

 filiform appearance is in part produced by the fact that the 



