THE DECAPOD CRUSTACEA. 165 



types. The differences between East and West are often 

 exceedingly striking, and cannot fail, for example, to 

 astonish anyone passing from the Firth of Forth to the 

 Firth of Clyde. One must suppose that in many cases it 

 is the warm currents which wash our western shores which 

 have carried the Mediterranean animals northwards, but the 

 fact that the shore on the West Coast is generally more 

 rocky than the East, and is often fringed by deeper water, 

 has no doubt also much influence. 



As Peneus is too rare to be described here, the first of 

 the Carididaa which we shall describe is the common prawn 

 (Palcemon serratus). This is the largest of our prawns, and 

 on certain parts of the coast, together with the much smaller 

 P. squilla, is the object of an important fishery. Both turn 

 bright red when boiled, and are so popularly distinguished 

 from the common shrimp, which merely turns a brownish 

 pink. A species of Palcemon may be instantly recognised 

 by the fact that each antennule bears three feelers, of which 

 two at least are very long, and by the fact that both the 

 first two pairs of feet are furnished with distinct forceps, 

 the second being much larger than the first. As other 

 characters we may note the large rostrum, which is strongly 

 toothed, and projects far forward between the eyes; the 

 position of the antennae, which are inserted beneath, and 

 only slightly to the outer side of the antennules ; and the 

 other characters incidentally noticed in the description of 

 the prawn. 



As to the species, on the East Coast P. serratus is not 

 very likely to be seen except in a fishmonger's, but on 

 certain parts of the coast young forms are not infrequent 

 between tide-marks. The colour is greyish, with spots and 

 markings of brown and red. The rostrum is very long, 

 longer than the large scale of the antennae, and turns up at 

 the point, forming a cruel-looking weapon. It has eight or 

 nine teeth above, placed near the base, and five or six 

 beneath. The filaments of the antenna?, and two of those 

 of the antennules, are very long, so that the trailing threads 

 are very conspicuous objects. The strong abdomen, with 

 its well-developed appendages, has already been noticed. 



The other common species of prawn (P. squilla, Fig. 47) 

 is also typically an inhabitant of deep water, but it occurs 



