No. 13. — On some Crustacean Deformities. By Walter Faxon. 



In November, 1879, the Museum bought of K. D. Atwood, a fish- 

 dealer of Portland, Me., a collection of nearly two hundred deformed 

 lobster claws. The malformations range from slight deformities result- 

 ing from incomplete restoration of lost parts, abnormal curvature of the 

 fingers, etc., to such as may, from the enormous development of abnor- 

 mal outgrowths or the duplication of parts, be truly called monstrosities. 

 Some of the most remarkable of these specimens are here described 

 and figured. One (Plate I. fig. 16) from the collection of the Peabody 

 Academy of Science, Salem, Mass., for which I am indebted to Prof. 

 E. S. Morse, a deformed claw of Callinectes hastatus from Chesapeake 

 Bay (Plate II. fig. 5) kindly communicated by Dr. S. F. Clarke, of Johns 

 Hopkins University, and an abnormal lateral spine of the carapace of the 

 sa^ ': species (Plate II. fig. 8) in the Museum of Comparative Zoology, 

 r > figured. Most of these irregularities have clearly resulted, as 



Eosel long ago remarked of similar malformations in the European cray- 

 fish, from injuries received after moulting, before the new cuticle had 

 become calcified. 



Plate I. Fig. 1 (right chela).* — In this claw the dactylus (a) is 

 curved strongly outwards towards the index, and thrust upwards from 

 its normal plane so that it does not meet, but crosses, the index when 

 closed. The prehensile power of the claw is thus destroyed. From the 

 inner border of the dactylus there is developed an enormous flattened 

 process, which divides at the tip into two prongs (b, c), which are 

 toothed on their opposed edges. Near the middle of the process is a 

 deep scar (d), visible on both sides. 



There is a specimen quite similar to this, for a drawing of which I 

 am indebted to Prof. S. I. Smith, in the Museum of Yale College, New 

 Haven, Conn. 



Plate I. Fig. 2 (left chela). — In this specimen the dactylus is curved 

 and bent from its true plane as in the last specimen. From the inner 

 edge of the dactylus (a) arise two diverging horns (b, c), which are fur- 

 nished with teeth upon their opposed edges, and simulate very closely 

 the dactylus and index of a normal claw. The dentition of the proximal 



* All the figures on Plate I. are Homarus Americanus, one half natural size. 

 vol. vin. — no. 13. 17 



