REPORT ON THE CRUSTACEA MACRURA. 97 



them to be pediform, cylindrical, biramose, terminating in a strong and sharp dactylos, 

 and furnished at the base with two subcylindrical vesicular branchiae : the seventh or 

 terminal pair of pereiopoda is considerably shorter than the others, it is five-jointed and 

 furnished neither with branchia nor ecphysis. 



Anteriorly the pleon corresponds in width with the posterior portion of the pereion 

 and tapers a little towards the caudal extremity. The external angle of each somite is 

 posteriorly rounded, and the telson approaches the form of that in the permanent or adult 

 stage, — being rounded and membranous at the extremity, and armed on each side with a 

 small sharp tooth. The pleopoda as yet are in an immature condition, consisting of a 

 stout peduncle and two slender subcjdindrical rami, except the posterior, which has the 

 peduncle short and the branches broad and foliaceous, making with the telson a well- 

 formed rhipidura. 



In neither of the specimens that belong to the Palinuridae have I seen any trace of a 

 branchial organ, but in those of the Scyllaridae I find them attached to all the legs from 

 the first pair of gnathopoda to the penultimate pair of pereiopoda, the ultimate, as in the 

 adult stage, being without any. Not only are they attached to the legs but some are 

 attached to the walls of the pereion also. Examination with a higher power shows that 

 those attached to the coxae of the leg;s are double-branched, while all the others are single, 

 but in pairs. Examination of the structure demonstrates that within these sacs the 

 future branchiae exist in the form of trichobranchiate plumes, excepting in those attached 

 to the coxae of the legs. These consist of two sacs attached at the base to one stalk ; 

 one of these sacs contains a branchial plume, the other a branchial lash ; the one becomes 

 the podobranchia, the other the mastigobranchia. The other sacs are evidently the 

 arthrobranchiate and pleurobranchiate plumes in an incipient state. 



Turning now to a very different stage of the young Palinurus, there will be found in 

 this Report one or two specimens that have reached the permanent form, and are 27 mm. 

 or scarcely more than one inch in length. 



Sir Walter Elliot captured at Waltair, on the coast of Coromandel, a specimen of 

 Palinurus that was only 18*25 mm. in length. It was smooth and opaline, with 

 antennae three times its own length. All its appendages were well-developed, and there 

 is little doubt that it was the young of some probably known species. 



If we compare this with the length of the large Phyllosoma of Palinurus, we find that 

 the smallest adult form is nearly half an inch shorter than the largest immature form, 

 and that the largest immature form has not yet sufficiently advanced in development to 

 possess branchiae; that the pleon, which in the adult condition is more than half the length 

 of the animal, is still in a rudimentary condition, the pleopoda as well as the rhipidura 

 being only in the early stage of gemmation (PI. XIIc. fig. 1 ). 



Judging, however, by the analogy of what we do see in the Phyllosoma of the closely 

 allied form of Scyllarus, we may safely infer that, corresponding with the development of 



(ZOOL. CHALL. EXP. PART LII. 1886.) Fff 13 



