AND OTHER BRITISH PRAWNS. 105 



1921 by Mr. 0. Hunt at Acle at a time of exceptionally high 

 tides. I have taken it myself at the following places : — 



K. Crouch at Burnham and Battlebridge. 



Blackwater at Maldon. 



Mersea Island. 



R. Stour at Harwich and Wrabness. 



R. Deben at Wood bridge. 



I was unable to find it in the Aide between Aldeburgh and 

 Iken, or in the Orwell at Pinmill, 



Breeding-period. 



In Norfolk the first eggs are laid about the end of May or 

 beginning of June. One female, taken on June 1 with eggs 

 apparently very recently laid, hatched her young on July 5,. the 

 eggs having therefore been borne .35-40 days. This result is in 

 general agreement with Mr. Elmhirst's figures *. Mr. Elmhirst 

 kept observation on L. squilla in rock-pools at Millport, and 

 found the period of development to depend on temperature as 

 follows : — 



Period of development. Average temperature. 

 1921 30 days 23° C. 



1911 40 days 14-5° 0. 



1912 56 days 11° C. 



Development may therefore be taken as requiring about 6 weeks 

 under usual conditions. 



Breeding continues actively through June and July. In 1921 

 it ceased about the middle of August, but in 1922 it was con- 

 tinued into the first week of September — a period of about 

 100 days. Each breeding female seems to produce two broods 

 in the season. In July females with eggs in an advanced stngeof 

 development always have the ovary distended with eggs of the 

 second brood, while in August the ovary is usually empty. The 

 production of two broods in the year was established by 

 Mortensenf for L. adspersus and by Ehrenbaum for Crangoyi vul- 

 garis, but Mortensen found that it only applied to the larger 

 prawns. In Norfolk, on the other hand, not only does practically 

 every female breed down to a size of about 30 mm., but the 

 majority, at all events, produce second broods. In July the 

 population of females may be separated into two groups — namely, 

 a small number of large prawns from 63 mm. to about 48 mm., 

 and the remainder of smaller prawns among which sizes of 

 36-39 mm. are the most frequent. These two groups no doubt 

 comprise prawns of two years' and one year's growth. The 

 former on July 25 for the most part bore eggs in early stages 

 having hatched their first brood, while a large proportion of the 



* Scottish Mar. Biol. Assoc. Auii. Rep. 1921, p. 7. 



t Vid. Uiidersog. paa Piskeriernes omraade udgivne af Dansk Piskeriforening, 

 i. (1897). 



