106 MR. R. GURNEY ON LEANDER LONGIROSTRIS 



one-year group carried eggs approaching hatching or showed 

 signs of having recently hatched young. It is probable, therefore, 

 that the older prawns spawn before the younger ones. 



The period of larval development has been ascertained by 

 Mortensen to be about 4 weeks in L. adspersus, and is probably 

 much the same for L. squilla. I have not been able to keep the 

 larva?, through more than one moult, so have no direct evidence 

 to offer. No post-larval prawns are to be found at Wells in July, 

 but about the middle of August they begin to appear, and become 

 abundant both in the marsh-pools and in the fucus growing on the 

 woodwork of the quay. In 1922, young did not become abundant 

 till the middle of September, but some then measured 22 mm. 

 and must have been in the harbour for some time. For the 

 most part the smallest young taken measure about 12 mm. 

 Since the young in the first and second post-larval stages do not 

 exceed 9 mm., it seems that metamorphosis occurs out at sea, and 

 that the young do not usually reach the shore till after three or 

 four moults. A very small proportion of the young prawns 

 found in September 1922 were either in the first or second 

 post-larval stages, and these must certainly have been brought in 

 by the flood-tide and have metamorphosed on the spot. On the 

 other hand, in spite of inuch search, I have only taken one larva 

 in Wells Harbour, and there can be no doubt that the whole 

 larval life is normally spent out at sea. This is in agreement 

 with Mortensen's conclusions with regard to L. adspersus. 



The proportion of adult males to females was only noted 

 accurately on two occasions — in Wells Harbour on July 25, 

 1922, and in Blakeney Harbour on August 10. In the former 

 case 37 males were found among 114 females, while in the latter 

 the males exceeded the females, the numbers being 69 males and 

 56 females. 



3. Leander adspersus Rathke. 



Palcemon rectirostris Zaddach, 1844. 



Falcemon leachii Bell, 1853, p. 307. 



Leander adspersus Yax.fahricii De Man, 1916. 



Colour. — Unlike the other British species of Leander, 

 L. adspersus has no bands of colour on either thorax or abdomen, 

 but the body appears of a uniform yellowish grey, due to small 

 black or reddish-black chromatophores scattered iri'egularly. The 

 rostrum is covered with chromatophores, which are concentrated 

 on the lower half in the form of red or sometimes pui'plish-red 

 blotches, which, as Kemp has pointed out, provides a conspicuous 

 feature by which the species may be recognized at a glance. The 

 long flagella and the peduncle of the antennule are also very red 

 and the legs banded with yellow, but without the blue on the 

 chela, which is so striking in L. squilla. 



Rostrum. — The rostrum usually extends well beyond the 

 antennal scales, is nearly straight, not very deep, and provided as 

 a rule with 6 spines above and 3 below in addition to the small 

 terminal spine. Only one of the dorsal spines is situated behind 



