REPORT ON THE CRUSTACEA MACRURA. 215 



that is reduced to a rudimentary condition, and it differs in this from the basecphysis 

 of the first pair. The coxa supports a rudimentary mastigobranchia that is reduced to a 

 membranous condition, and the podobrauchia is wanting. 



The first pair of pereiopoda is slender, chelate, and has the carpos very long and 

 slender and the propodos short. 



The second pair of pereiopoda is also slender and chelate, but longer and more 

 robust than the first, it has the carpos very long, nearly as long again as the propodos, 

 the pollex of which is straight and continuous, as is also the external margin of the 

 dactylos ; the whole appendage is sparsely fringed with long hairs. 



The third pair of pereiopoda is chelate, but has the carpos short, triangulate, the pro- 

 podos large and thick, the palm being nearly as broad as long, and, the anterior or outer 

 margin serrate with teeth that gradually increase in size as they approach the dactyloid 

 articulation. Minute denticulations arm the external margin of the dactylos as well as 

 that of the pollex ; intermingled with these are a few long hairs. 



The two following pairs of pereiopoda are long, slender, and terminate in a tridentate 

 dactylos. They have the carpos longer than the propodos. 



The pleon is tolerably robust, and all the somites are acuminate at the centre of the 

 lateral margin of the coxal plates, and the telson (z) is ovate, serrate at the margins and 

 furnished with two serrate carinae that longitudinally traverse the dorsal surface, one on 

 each side of the central fine. 



The branchial arrangement is peculiar. The plumes increase considerably in size as 

 they recede posteriorly. The podobranchial plume is wanting in each except the first 

 pair of pereiopoda, where a feeble one is attached to a small mastigobranchial plate. 

 The mastigobranchial plates are present in all except the posterior pair of pereiopoda ; 

 they gradually increase in size as they proceed backwards from the first pair of gnatho- 

 poda. The arthrobranchise and pleurobranchiaa, which are small and almost rudimentary 

 on the first pair of gnathopoda, increase gradually in size until the fourth pair of pereiopoda 

 is reached ; with the fifth pair the pleurobranchial plume alone is present, but that has 

 become so much developed that it reaches to the anterior margin of the branchial 

 chamber, (3c) ; that of the fourth pair of pereiopoda, as well as the arthrobranchnp, is 

 nearly as large, and is horizontal and anteriorly directed. The arrangement may best be 

 seen in the following table : — 



Pleurobranchise, 

 Arthrobranchiae, 

 Podobrancbias, 

 Mastigobranebiae, 



Observations. — De Haan has classified this genus as belonging to the family Penseida?, 



