774 PROF. T. H. HUXLEY ON THE CLASSIFICATION [June 4, 



approach the characters of the branchiae of the Lobster. The groove 

 on the inner face of the stem seems, at first, to be reduced to nothing 

 in the upper part of the podobranchiae. However, a transverse 

 section (fig. 7, m) shows that it exists and is bounded by two lips, 

 the anterior of which is produced into a narrow ala. But the 

 numerous hooked branchial filaments, which arise from the posterior 

 face of the stem, fill the groove and appear to obliterate it. 



The hindermost of the arthrobranchiae is attached close to the 

 articulation of the coxopodite with the epimeron, and is therefore 

 in the same position as one of the anterior series of arthrobranchiae 

 in other Crayfishes. There is not the slightest trace of the attach- 

 ment of another brauchia on the arthrodial membrane behind this. 

 But on the epimeron, just above the margin of the articular cavity, 

 and (H inch behind the root of the anterior branchia, a minute 

 filament, 0'05 in. long, which I take to be a rudiment of the posterior 

 branchia, enclosed by the downward extension of the epimeron, 

 projects. 



The attachment of the next arthrobranchia is like that of its pre- 

 decessor, but not quite so far forward. At a distance of 05 in. 

 behind and above its root, an exceedingly minute papilla, not more 

 than a fifth of the length of the foregoiog, is enclosed in the arti- 

 cular edge of the epimeron. This is doubtless the rudiment of the 

 posterior arthrobranchia. The three remaining arthrobranchiae are 

 fixed into the arthrodial membranes of the other ambulatory and 

 prehensile limbs, in a position corresponding with that occupied by 

 the fourth. In the case of the hindermost of these, or that of the 

 eleventh pair of appendages, there is, above and behind the root of 

 the gill, and OU8 inch distant from it, a filamentous rudimentary 

 branchia, rather less than Ol inch long, attached within the articular 

 margin of the epimeron. Three or four minute unequal processes 

 are given off from the posterior edge of this filament. There is 

 another very small papillary rudiment immediately above and behind 

 the root of the next arthrobranchia ; but none could be discovered 

 above that of the most anterior arthrobranchia. 



In addition to the five conspicuous and functional outer arthro- 

 branchiae, there was another very small one, only 0* 18 inch long, and 

 almost rudimentary, attached to the second maxillipede. 



The pleurobranchia of the last thoracic somite was only 0*3 inch 

 long, and was hardly visible at first, from being overlapped by the 

 hindermost podobranchia. I could not discover the slightest trace 

 of any other pleurobranchiae. 



The upper part of the modified podobranchia of the first maxillipede 

 is sharply folded upon itself longitudinally ; and its outer lobe is beset 

 with numerous short branchial filaments, most of which have ter- 

 minal hooks. Similar hooked filaments are to be found about the 

 base and the posterior region of the other podobranchiae ; but a large 

 proportion of the filaments of these branchiae, and all of those of the 

 arthrobranchiae, appear to be hookless. 



The tubercles of the coxopodites give rise to small tufts of short 

 and straight setae, which are hooked at the end, like those of Asia- 



