118 MR, R. GURNEY ON L^jANUER LONGIROSTRIS 



For instance, among 30 specimens of L. squilla from Wells one 

 possessed three of these setse. Among ten L. serrattis from 

 Poole one was found not only with four setas, but with an 

 additional terminal spine (text-fig. 4 E). 



Distribution. — As is well known, P. varians inhabits fresh water 

 in the Mediterranean region and brackish or salt water on the 

 North Sea and Atlantic coasts, but it is not exclusively a fresh- 

 water species even in the Mediterranean region, since it is 

 recorded by Gourret* in salt water in the Etang de Thau and 

 Etang de Berre on the south coast of France, in company with 

 strictly marine species such as Leander xiphias. 



The distribution has been fully described by Barrois f, but may 

 be briefly repeated here with some additions. 



In fresh water it is recorded from several of the Italian lakes, 

 Venice, Dalmatia, Montenegro, Scutari, Corfu, Turkey, Egypt, 

 and Mesopotamia. According to Pesta, Allocaris sinensis is only 

 a variety of this species, its distribution being thereby extended 

 to China (Pekin). It has been found in a hot spring at San 

 Giuliano, near Pisa, at a temperature of 28"75° C. In Tunisia 

 it is said to be very common in fresh waters in the south 

 (Gabes, Tozeur, &c.), and has even been found in water at a 

 temperature of 25^ to 27° C. I have taken it myself in a stream 

 near Biskra in the Algerian Sahara. 



In salt or bi'ackish water it has been found in the Etangs de 

 Berre and Thau (S. France), the Black Sea, Seine Estuary, 

 Boulogne and Pas-de-Calais, coasts of Holland and Friesland, 

 Portugal, Denmark, North Germany and Sweden. 



In Britain it is probably widely distributed. It is recorded 

 from several localities on the coast of Devon, Dorset, and Corn- 

 wall, and seems to occur all round Ireland. It has also been 

 taken in the Isle of Wight, on the Northumberland and Durham 

 coasts, and by the estuaries of the Forth and Clyde in Scotland. 



In Norfolk the great stretch of salt marsh between Thornham 

 and Salthouse is eminently suited to the requirements of 

 P. varians. These marshes are seamed with muddy creeks which 

 are empty at low tide, but the marsh between lies for the most 

 part above the level of spring tides. Dotted over this marsh are 

 innumerable small pools full of brackish water, and in almost 

 every one of them these prawns are to be found. Late in autumn 

 the young of the year swarm in these pools, having reached a size 

 of about 20 mm., but in June, when maturity is reached, the 

 numbers have decreased most strikingly, showing a great mor- 

 tality during winter and spring. When breeding begins, the 

 water in some pools may become almost thick with larvae, very 

 few of which probably survive even to the post-larval condition, 

 since the available food must be rapidly used up. In two pools 

 at Blakeney examined in June large numbers of larvse were found 

 together with quantities of the Copepod, Eurytemora lacinulata. 



* Ann. Mus. Hist. Nat. Marseille, v. (1897). 

 t Bull. Soc. Zool. France, xi. (1886). 



