76 Proceedings of the EoyoZ Physical Society. 



I. Carcinus m^nas. — a. (PL IL, Fig. 1) In the specimens 

 shown I have placed the normal right foot of the anterior pair 

 alongside of the left foot, in which the exaggerated variation 

 and partial distortion occur. In the abnormal form the joints, 

 and especially the so-called arm, wrist, and hand joints, 

 are larger than in the other, while the jointed finger is more 

 slender. The abnormity consists of a pair of pretty taper- 

 ing, sub-crescent shaped, toothed, yetunjointed fingers spring- 

 ing from the base of the jointed finger of the hand {chela). 

 These are little more than fths. of an inch long, and a little 

 less wide at the broadest part — the slender points of the cres- 

 cent being fths. of an inch from each other. A furrow, com- 

 paratively broad at the arc of the crescent, tapers gradually 

 on both sides, till about a line from the points. The width 

 between the tip of the unjointed finger and the outermost 

 tip of the crescent is fths. of an inch. The whole length of 

 the foot is 1 inch and fths. (5.) The second instance of 

 abnormal growth occurs in the third pair of feet of the same 

 species, but in a larger and older specimen than that just de- 

 scribed (Fig. 2). At the tip of the penultimate joint a rounded 

 process, fths. of an inch in length, proceeds in the natural 

 direction of the last joint, but instead of tapering to a point, 

 it bifurcates near the tip — the forks showing indistinct traces 

 of toothing. This process is thickest at the base, and to this 

 the last joint, which is of the natural size and shape, is solidly 

 attached almost at right angles to it. I have placed the 

 natural joint of the unaltered right limb alongside of this 

 one for contrast. 



II. Cancer pagurus. — (a) Abnormity in the stout an- 

 terior left foot (Fig. 3). This specimen has written on it an 

 honoured name, " Ch. W. Peach ; locality, Cornwall." The 

 divergences from natural growth on both the specimens, for 

 which I am indebted to Mr B. JST. Peach, of H.M. Geological 

 Survey, are connected with the jointed or external limb of 

 the forceps. At the base of this, and at right angles to it, a 

 rounded process, more than an inch and a half in circumfer- 

 ence, is solidly united. At about an inch from its root it 

 bifurcates, like the corresponding abnormal growth in Car- 

 cinus mcenas, each of the forks being distinctly toothed. The 



