SOUTH DEVON AND COHNWALL MAEINE FAUNA AND FLORA. 281 



Pagurus, we are inclined to believe in a near resemblauce of their larvae. 

 Hence onr assumption that this present immature species is a young Pagurus. 



The next stage (PL I. fig. 3) to which we allude is one that we noticed 

 in our preliminary Heport to this Association. 



The animal is a small creature that we took floating near the siirface of 

 the sea in a warm day in June. Its general appearance is that of a j'oung 

 maerurous crustacean ; and as such has been classified near to CaUianassa and 

 Calliadina. It is symmetrical, except in the larger development of the great 

 chela of the right side. The two succeeding pereiopoda are very long, but 

 simple, in their formation. The last two are considerably reduced in size ; and 

 the anterior terminates in a small imperfectly didactyle forceps ; and the pos- 

 terior has a copious brush, consisting of cilia and short and broad spines, 

 amongst which the short obtuse and spinous dactylos is discernible. The 

 pleon is well developed, having each somite clearly defined, and all, except 

 the first, carrying an equally developed pair of appendages, each of which 

 consists of a peduncle and two unequal rami. The posterior pair, or uropoda, 

 differ from the others in having the peduncle shorter, and the outer ramus 

 longer and more robust ; it is likewise, in the older specimens, curved slightly 

 more on the left side than on the right. 



In this condition they probably continue untU they find a suitable molluscous 

 shell in which to reside. We imagine that they may continue to cast their 

 exuvia and grow according to the length of time that they are deficient of such 

 shell, because we have taken specimens occupants of shells that are stiU smaller 

 than the one described, and yet further advanced to maturity. It would be 

 curious to see if, when deprived entirely of the use of a shell for a habitat, 

 they shoiild continue to grow and retain the normal form of the pleon gene- 

 rally — a feature that characterizes some of the exotic closely allied genera. 



Thus a careful examination of numerous specimens has enabled us to 

 demonstrate the progressive development of the genus Pagun(S, and to affirm 

 with much confidence, judging by the descriptions and figure of the authors, 

 that the genera Ghucothoe of M. -Edwards, and Prophylax of LatreiUe, are 

 none other than an immature stage of the genus Pagurus ; but since their 

 specimens were exotic, they were probably the yoimg of some foreign species. 



Amongst the maerurous Crustacea, we have had the opportunity of exa- 

 mining and figuring the larva of Palinurvs (PI. II. fig. 2). The young of this 

 genus was first made known to this Association by the late Mr. E. Q. Couch 

 of Penzance, at the Meeting at Dublin in 18-57, when he drew attention to the 

 near resemblance existing between it and the genus Phjlhsoma. In ] 864-65 

 M. Gerbe (see the ' Comptes Eendus ') repeated the discovery of Mr. Couch, 

 and asserts that the larva of PaVmurus is identical with the genus Phyllosoma. 



The larva of most of the decapod Crustacea has the largest amount of deve- 

 lopment, commencing with the cephalon and the pleon ; whilst in the larva 

 of the Palimirus the greatest advancement exists in the anterior part of the 

 cephalon and in the pereion, whereas the pleon is almost rudimentary. 



On comparing it with the genus Phyllosoma (PI. II. fig. 1), as M. Gerbe 

 has done, there is little in the general structure of the animals that can war- 

 rant a separation of the two, or that might not be accounted for by an 

 increasing development of the younger specimens. Yet there are certain 

 points that weigh heavily in the balance of evidence against the larva of Pa- 

 linurus and Phyllosoma being but different stages of the same animal : — 



(1) It is contrary to our experience that so small an amount of progressive 

 development shall have taken place in an animal that has increased in 

 growth to about thirty times its size. We generally perceive in the develop- 

 ment of Crustacea that the most important changes are those that imme- 



