ORDER DECAPOD A — PAGURUS. 19 



GENUS PAGURUS. Fabricius. 



Anterior part of the body crustaceous ; the lower long and cylindrical, soft, and rolled upon 

 itself. Interior antenna? short, bifid at the tip, and scarcely reaching beyond the peduncle 

 of the external antennae. Extremity of the tail with an unequal pair of appendices. 



Obs. This genus, which is at present subdivided into four others, now comprises nearly 

 fifty species distributed throughout the world. They are all in the habit of occupying the 

 dead shell of a univalve, which is exchanged for a larger one as they increase in size. This 

 singular habit has suggested the popular name of Hermit Crab. Some species live on land, 

 occupying of course univalve terrestrial shells. 



Pagurus pollicaris. 



plate viii. fig. 21. 

 (state collection.) 



Pagurus pollicaris. Sat, Journ. Acad. Nat. Sciences, Vol. 1, p. 163. 



P. id. Milne-Edwards, Hist. Nat. des Crustacea, Vol. 2, p. 237. 



P. id. GorjLD, Invertebrata of Mass. p. 329. 



Description. Anterior segment of the thorax subcordate ; truncate behind. Eyes on pedi- 

 cels 0'3 long, with a small pointed scale at the inner base. Interior antennae shortest ; the 

 penultimate joint extending beyond the ocular pedicels. External antennae 1 ■ 2 long ; the last 

 joint composed of about sixty articulations, with a long spinous appendix at its base, nearly 

 as long as the ocular pedicels. Hands unequal, opposed ; the right one nearly twice as long 

 as the left, much compressed, crested ; the upper ridge convex, dentate ; the finger longer 

 than the thumb, with a series of tubercles becoming double towards the angle. Thumb with 

 a stout projection or knob beneath, giving a rectangular appearance to the lower part of this 

 member, and with about eight tubercular teeth. Left hand similar to the right, but wanting 

 the tubercular knob beneath. Both hands, together with the carpus and succeeding joints, 

 strongly tubercular, not hairy. Thighs of the second and third pair smooth below, tubercular 

 above. Carpus of the right not as long as the hand, above rounded ; of the left, angular. 

 Terminal joints of the second and third pair slender, nearly equal in length to the two pre- 

 ceding joints, compressed, ciliate on the two edges, with a double series of punctures and a 

 medial impressed line. 



Color, red when recent ; pearly grey in cabinet specimens. 



Length of the thorax, 0"5 ; of the right hand, 0-8. Width of the same, 0*6. 



This is the largest American species that I have seen. It is frequently found in the shell 

 of the Fulgur carica. It is rare to meet with a perfect specimen, as they are frequently 

 found deprived of their antennae, and of one or both their eyes. This is attributed by iisher- 



3* 



