0)1 Abnormal Appendages in Crabs. 399 



XLV. — Two Cases of Abnormal Appendages in Crabs. 

 By W. T. Calman, D.Sc. 



(Published by permission of the Trustees of the British Museum.) 



Among the specimens of Crustacean abnormalities that have 

 been added to the British ]\Iusoum collection in recent years 

 are two that seem especially deserving of record. The first 

 is a case of incomplete homoeosis, between limbs that are 

 not adjacent, in Cancer pagur us; the second is an example 

 of duplicity, of a type hitherto unknown, in a cheliped of 

 Portunus puber. 



1. Homoeosis in Walking-leg o/" Cancer pagurus, Linn. 

 (Fig. ], p. 400.) 



Tlie specimen is a male, measuring 238 mm. in width of 

 carapace, and comes from Dartmouth (B. M. Crust, reg. 

 no. 1913. 2. 12. 1). It is perfectly normal except as regards 

 the second walking-leg (sixth thoracic appendage) of the left 

 side, which carries a chela resembling, but smaller than, that 

 of the normal cheliped. 



The coxa of the abnormal limb does not differ from that 

 of the corresponding limb on the other side of the body. 

 The basi-ischium is somewhat loosely articulated with the 

 coxa, so that the posterior condyle can be raised a little Avay 

 out of the articular notch. Distally the basi-ischium is a 

 good deal wider than that of the normal limb and somewhat 

 inflated on the ventral surface. The merus is shorter and 

 wider than the normal, its length being about 58 mm. and 

 its greatest width 32 mm., while the corresponding measure- 

 ments in the limb of the opposite side are 70 and 24 mm. 

 respectively. The distance between the distal articular pro- 

 cesses is greatly increased for the reception of the carpus. 

 The carpus is shaped much as in the normal cheliped, 

 except that its outer (dorsal or extensor) face is flattened ; 

 its greatest length is 42 mm. and its depth distally 30 mm. 

 The propodus, compared with that of the normal cheliped, 

 appears somewhat shrunken and malformed. It measures 

 about 48 mm. in length to the articulation of the dactylus 

 by about 30 mm. in depth and 17 mm. in thickness in the 

 middle ; the greatest depth is at the articulation with the 

 carpus and the greatest thickness at the articulation with 

 the dactylus. The immovable finger is bent downwards at 



