chap, xxi.] CRUSTACEA : EXCEPTIONAL CASES. 



537 



Without having seen the specimen it is impossible to say much, 

 but the parts should be examined with a view to this possibility. 

 I conceive that the large spine marked by Faxon &p' stands on 



1B' + L' 



Fig. 194. Homarus americanus, No. 826. A right chela. (After Faxon.) 



the morphologically middle line between the two extra half- 



meropodites.] Faxon, Harv. Bull VIII. p. 262, PI. II. fig. G. 



*827. Astacus fluviatilis $ : large adult. /. 



Abdomen wide in comparison with 



slender chelae: otherwise normal except 



left chela. This was formed as in Fig. 



195. All normal except carpopodite, 



from which arose a fixed piece seeming 



to be an extra misshapen carpopodite, 



bearing three extra chelce, L', R and x. 



[R! and L' are a clear pair of images L' 



being right and left respectively. But 



between R' and the normal L there is 



the third extra chela x. As to the 



nature of this nothing can be said. 



Whether it is a left or a right cannot 



be told from fig. So far as I know, Fk;. 195. A$tacu» fluviatilis $Ho. 



this case is unique. Full description 82 ?, 1(,ft chela. /.. the normal. 7/ . 

 on j w,^nm,^,.^v,4.„ • • • • i L>', presumaMv extra right and lelt 



and measurements given in original, oh ^ *, exta-a chela of uncertain 



q. V.] CANTONI, Rend. R. 1st, Lomb., nature. (After Cantoui.) 



1883, xvi. p. 771,^. 



