472 ROBERT GURNE7. 



The pleopods ave now well developed, eacH exceeding the 

 length of the next succeeding segment. The first four pairs 

 consist of a broad basal part bearing a long exopodite and a 

 short stump representing the endopodite, but there are no 

 setae and no trace of segmentation. The fifth pair, on the 

 sixth segment, are simple unbranched appendages. The 

 telson is exactly the same as in the preceding stage. 



The Megalopa (fig. 13). — Measurements (average of ten 

 specimens) : 



Length of carapace . . . 3'6 mm. 



Breadth across third lateral spine . 3"1 „ 



Length of antenna? . . . 4*5 „ 



The last larval stage passes by a single moult to the 

 Megalopa, which is distinctly recognisable as Corystes, 

 though retaining certain features characteristic of the zocea. 



Hie rostrum and dorsal spine are still j^resent, though very 

 greatly reduced. 



The rostrum has now the form of a broad plate extending 

 forwards between the eyes, its lateral margin arched upwards 

 and crenulated. Its extremity is trifid, the median process 

 representing the last trace of the original long rostral spine 

 and retaining the orange chromatophores of the previous 

 stage, the lateral processes by which it is flanked being new 

 formations. A few hairs are borne upon the upper anterior 

 surface of the rostrum. 



'Hio dorsal s})iue is now an inconspicuous orange-red 

 process, situated not immediately over, but somewhat behind 

 the heart. From it a ridge runs forwards for some distance 

 along the middle line of the carapace. 



On either side of the middle line, in the region of the 

 stomach, there is a single short spine on the dorsal surface. 

 These spines appear first at this stage, and arc lost again 

 with the next moult. 



Laterally the carapace bears three strong teeth on cither 

 side, the first iunuediately behind the eye, and the third 

 above the first ambulatory leg. The pustero-lateral margin 



