INTRODUCTION. liii 



at the bottom of the vessel, to cast their shells, and 

 acquire a new form. They are exceedingly delicate, and 

 require great care and attention to convey them through 

 the first stage; for unless the water be supplied very 

 frequently and in great abundance, they soon die. The 

 second form of transmutation is equally as remarkable as 

 the first, and quite as distinct from the adult animal (d). 

 In the species now under consideration this second trans- 

 formation is marked by the disappearance of the dorsal 

 spine ; the shield becomes flatter and more depressed, 

 the anterior portion more horizontal and pointed, the 

 three festoons having disappeared. The eyes, from being 

 sessile, are now elevated on footstalks ; the infra-orbital 

 appendages become apparently converted into antennae. 

 The claws undergo an entire revolution; the first pair 

 become stouter than the others, and are armed with a pair 

 of nippers," the others being simple ; " but the posterior 

 pair are branched near the base, and one of the branches 

 ends in a bushy tuft. The tail is greatly diminished 

 in its relative size and proportions, and is sometimes 

 partially bent under the body, but is more commonly 

 extended. This form is as natatory as the first. They 

 are frequently found congregating around floating sea- 

 weed, the buoys and strings of the crab pot marks, and 

 other floating substances, both near the shore and in 

 deep water. Their general form somewhat resembles a 

 Galathea." 



Every one will immediately recognise in this descrip- 

 tion, and in the figure which accompanies it, the creature 

 typifying the genus Megalopa of Dr. Leach. Here, then, 

 is the second form of a brachyurous type, and its final 

 change is seen in the accompanying figure (e). It is 



