OF CRUSTACEA. 277 



mity of the tail also differs from that of every other with which 

 I am acquainted, in being spatulate and very deeply fringed. 



I beg here to repeat that my proofs of metamorphosis in the 

 Brachyura extend to the repeatedly enumerated genera of 

 Cancer (Zool. Res.), Carcinus, (Memoir just sent to the 

 Royal Society), Portimus, (accompanying Memoir,) Pinno- 

 theres, (Ent. Mag.), Porcellana, (above given,) Gegarcinus, 

 Thelphusa, Eriphia, Inachus, and Pagiirtis. In the Ma- 

 croura to Homarus, Palcemon, Crangon, Astacus, and 

 Galathea. 



In regard to the changes which the crabs undergo after 

 their last metamorphosis, and to which Mr. Westwood alludes, 

 I agree with that gentleman that we as yet want facts to guide 

 us. That they still differ from their parents in the form of their 

 clypeus, and in its indentures (at least in Carcinus,) is evident 

 by an inspection of the figure which accompanies my Memoir 

 now before the Royal Society ; and by a careful perusal of my 

 notes, I find the following additional information, viz. — 



" On the second change, the projection in front between the 

 eyes disappears, and the five denticulations at the sides become 

 more marked, with a very slight widening of the clypeus at 

 this part ; the inner pair of antennas are also more developed 

 and conspicuous. On the third change, the clypeus dilates a 

 little more, the three posterior denticuli appear spinous, the 

 two anterior ones remaining obtuse." 



It is therefore certain that another, or fourth change, is 

 required in this individual before a naturalist could pronounce 

 as to its species by a simple comparison with the parent crab. 



I 



Metamorphosis in Portunus. 



Having, in a Memoir which has been laid before the Royal 

 Society, made known the particulars of the double metamor- 

 phosis in the Brachyura (crabs) as observed in Carcinus 

 mcenas, in which these curious changes of form and structure 

 have been traced in as complete and satisfactory a manner as 

 the case probably admits, so as to render quite evident that 

 the young first present themselves to our notice as Zu'ea, and 

 that they assume a second intermediate form, or that of Mega- 

 lopcp, previous to their taking on that of their parent ; 1 have. 



