64 



DISCOVERY REPORTS 



Mastigopus I. Length 3-15 mm. Rostrum 0-55 mm. 



Supraorbital, hepatic and posterior dorsal spines present, but no marginal. Dorsal 

 organ very small. 



Abdomen with minute dorsal spines on somites 1-3, those of 4 and 5 larger; spine 

 on somite 6 minute. Minute pleural points on somite 4 and larger on somite 5 ; none 

 on somites 1-3. Median ventral spines on somites 1-4. Telson short, as in S. vigilax. 



Eye of same form as in Acanthosoma, with same dark area in the pigmented part. 

 Mandible without palp. Legs without trace of exopods. Legs 4 and 5 vestigial. Pleopods 

 without endopods. Exopod of uropods, setose part five times as long as bare part and 

 about seven times as long as wide. 



Remarks. Hansen has described (19 19, p. 25) the Acanthosoma of S. orientalis which 

 is very closely allied to 5. edzvardsi and seems to replace it in the Pacific. So far as can 

 be seen from his figures and description the Acanthosoma is almost identical with that 

 of S. edzvardsi. He does not, however, mention the median ventral abdominal spines. 



TABLES OF MEASUREMENTS 



The following tables of measurements show clearly some of the differences between 

 species in shape of eye and its length in proportion to the body, and in the proportion 

 the setose part of the outer margin of the uropod bears to the bare part. Where sufficient 

 specimens are available the changes which take place with growth are shown. These 

 measurements reveal much individual variation, and it must be confessed that they are 

 open to the objection that the proportion of eye to body cannot be entirely accurate 

 owing to the difficulty of measuring the body correctly when, as is generally the case, 

 it is bent nearly double. 



The specimens of S. corniculum measured include more than one species, but we have 

 been unable to separate them with certainty. Those marked * and ** have been examined 

 by Mr Burkenroad and are regarded by him as probably representing two different 

 species. 



Measurements of Mastigopus 



