520 ME. K. I. POCOCK ON THE 



The characters which, have been rnost used for distinguishing 

 the species are : (1) the number of legs, (2) the form of the skin- 

 papillfe, (3) colour, and (4) the dentition of the jaws. The last 

 is troublesome to determine, and is not on that account likely 

 to be very much patronized, and unless its validity has been 

 tested iu a large number of cases it should be employed with 

 very great caution *. Colour unfortunately is very liable to 

 destruction by the alcohol. So, too, does the form of the papillae 

 seem to be affected by this preservative. These papillae are con- 

 tractile processes of the skin : when distended they in nearly all 

 cases are seen to consist of a conical or cylindrical basal portion 

 tipped with a slender, subcylindrical, setiferous distal portion ; 

 when contracted they are rounded and dome-shaped, with a 

 distinct circular depression on the summit ; at intermediate 

 stages the distal portion appears like a button-shaped cap upon 

 the basal portion ; moreover it appears that the shape of these 

 organs may be different when they are viewed from the front and 

 the side. All these facts point to the conclusion that the form 

 of the papillae cannot, at present at least, be greatly relied upon 

 for distinguishing the species. As for the number of the legs, 

 they differ according to sex, and vary within undetermined limits 

 in the sexes. 



These considerations will show how purely provisional must 

 be regarded all our conclusions respecting the validity of the 

 species enumerated below. 



Peeipattjs JULiroRMis, Guilding. 



P. juhformis, Guilding, Zool. Journ. ii. p. 443, pi. 14(1826); also in 

 Isis,xxi. p. 168, pi. ii. (1828) ; Sedgwick, Quart. Journ. Micr. Sci. xxviii. 

 p. 478 ; Pocock, Nature, vol. 46, p. 100. 



P. Edwardsii, Sedgwick, op. cit. pp. 467-473 (? Edwarsii, Blanchard). 



Colour (in alcohol) : the dorsal surface varying from almost 

 black to a greyish brown or fawn ; viewed with a lens, distinctly 

 mottled, the mottling being attributable to the circumstance 

 that the papillae are of a paler tint than the skin which supports 

 them ; there is a dark more or less clearly defined uarrow median 

 dorsal longitudinal band, this band being apparently mostly 

 due to the discontinuity of the papillae across the middle line 

 of the back, which permits the darker colour of the skin to be 



* I refer here merely to the small series of teeth on the inner blade of the 

 jaw. 



