390 DISCOVERY REPORTS 



In Spirontocaris polaris the first larva has the antennule fully segmented, with small 

 inner branch ; the antennal scale has the apical spine, and no segmentation ; supra-orbital 

 spines are present ; the exopods of the maxillipedes (they are absent from all legs) have 

 four symmetrically placed apical setae (Stephensen). 



The most remarkable feature of shortened development is the apparent difficulty of 

 eliminating the three first obligatory stages of the normal larva. In normal development 

 the uropods appear almost without exception in stage III, and, however fully the free 

 larva is provided with pereiopods, or even pleopods, when hatched, the uropods are 

 never present. In the few cases in which the course of abbreviated development is 

 satisfactorily known the uropods appear, as in the normal larva, in stage III even if the 

 adult form is to be attained at the next moult — for example, Palaemonetes varians 

 lacustris, Palaemon potiiina (SoUaud, 1923). Even more striking is the fact that in 

 Astacusfluviatilis, although the young on hatching have all the appendages more or less 

 of aduh form, still the uropods do not appear till stage III. In ScJerocrangon, although 

 the young hatch in the adult form, and attach themselves to the parent, the embryo 

 just before hatching has no uropods (Wollebaek, 1906). 



SARON MARMORATUS (OLIVIER) AND ALLIED FORMS 



Saron marmorattis is not uncommon on the coral reefs at Ghardaqa, and two females 

 hatched their eggs in the laboratory. A close similarity was at once noticed between 

 these larvae and others which were at the time common in the plankton, and it was 

 assumed at first that all belonged to this species. They were all characterized by their 

 rich colour, generally red, and compact form, with small posterior tooth on the carapace. 

 It was not possible to spare the time necessary for detailed examination, but it became 

 evident later that there must be at least two species present, though they could not be 

 easily distinguished without risk of injury to those which it was desired to keep alive. 

 I was also singularly unfortunate in getting these larvae to moult to post-larval. Exami- 

 nation of the preserved material shows that there are actually at least three distinct 

 forms, and that the material does not admit of separating them into series. It is also 

 impossible to determine with sufficient certainty that any of the later larvae belong to 



Saron. 



The close resemblance of these larvae to Latreutes (Gurney, 1936) is evident, but they 

 all lack the dorsal spines present on abdominal somites 4 and 5 in L.fticoruni, and also 

 the spine present in that species in the middle of the margin of the carapace. They 

 agree in general form, in shape of telson and in the presence of a small tooth at the 

 posterior angle of the carapace. Further, the fact that in all these forms there are four 

 apical setae on the exopods is an important point when we take into account the fact 

 that there are three in all other Hippolytidae known. I have given below a description 

 of a larva from the Barrier Reef which I attribute with some doubt to Latreutes, for the 

 sake of comparison with the Red Sea larvae. 



It is quite certain that these larvae all belong to closely related species of Hippolytidae, 



