ioo SPECIAL CONVERGENCE 



described Pentanymphon during the National 

 Antarctic Expedition in the Discovery, and 

 redescribed Decolopoda from material procured 

 by Mr W. S. Bruce during the Scottish National 

 Antarctic Expedition in the Scotia, shows the 

 radical differences which exist between the two 

 genera simultaneously with the numerical con- 

 vergence of the ambulatory appendages. The 

 differential characters indicate the respective 

 places of the genera in the system of Pantopoda ; 

 the convergent character gives no indication of 

 their affinities to any existing forms. 



TABLE OF CONVERGENCE IN PANTOPODA. 

 PENTANYMPHON. DECOLOPODA. 



1. Ambulatory appendages, Ambulatory appendages, five 

 five pairs. pairs. 



2. Body elongate, clearly Body short, obscurely seg- 

 segmented, very slender, with mented, broadly elliptical in- 

 lateral processes widely separ- eluding the lateral processes in 

 ated. the contour of the ellipse. 



3. Proboscis cylindrical, Proboscis clavate, bent down- 

 straight, much shorter than the wards, longer than the body, 

 body. 



4. Mandibles chelate, 2- Mandibles chelate, 3-jointed. 

 jointed. 



5. Palps 5-jointed. Palps lo-jointed. 



6. Ovigerous legs, lo-jointed, Ovigerous legs, 10- jointed, 

 formed plainly as in Nymphon. looped as in Colossendeis. 



7. Abdomen small, ovoid, Abdomen long, slender, sub- 

 directed obliquely upwards. clavate. 



by T. V. Hodgson : I. " On a New Pycnogonid from the South 

 Polar Regions," Ann. Nat. Hist. (7), xiv., 1904, pp. 458-462, pi. 

 xiv. 2. "Scotia Collections. On Decalopoda australis Eights, 

 an old Pycnogonid rediscovered," Proc. Roy. Phys. Sac., Edin- 

 burgh, vol. xvi., 1905, pp. 35-42, pi. iii. 3. " Decalopoda and 

 Colossendeis," Zool. Anz., xxix., 1905, pp. 254-256. [The accepted 

 spelling of the former name is now Decolopodal\ 



