No. 13. — On some Orustacean 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- 
ma] outgrowths or the duplication of parts, be truly cálled 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 IT. fig. 5) kindly communicated by Dr. S. F. Clarke, of Johns 
Hopkins University, and an abnormal lateral spine of the carapace of the 
same species (Plate II. fig. 8) in the Museum of Comparative Zoólogy, 
are also figured. Most of these irregularities have clearly resulted, as 
Rósel 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. VIII. — NO. 13. Mg 
