THE GRAPSOID CRABS OF AMEBICA. 115 



united in one piece; in the female abdomen the segments are usually 

 all free. 



Found only in America, where, so far as known, it lives on the 

 outside of flat sea-urchins, its bifurcate dactyls enabling it to cling 

 to the spines of the urchin. 



Remarks. The four new species are dedicated to those British 

 carcinologists whose work has contributed most to a knowledge of 

 the classification of decapod crustaceans. 



The outer maxiliipeds of the seven species fall into two distinct 

 groups. In one group the distal portion of the merus is suboblong, 

 its distal margin more or less truncate, while the palpus is of con- 

 siderable size relatively, the carpus and propodus nearly equal in 

 size, the latter quadrilateral, in two instances bearing a minute 

 dactylus at the distal inner corner, in two instances lacking a dacty- 

 lus, though in nitidus there is evidence of a rudiment. In the other 

 group the distal portion of the merus is suboval, narrowing to the 

 extremity and the palpus is very small, its three joints rather 

 squarely end to end. 



The form of the palpus is very difficult to determine in this genus 

 as it is usually folded in a groove in the edge of the merus, and the 

 segments, especially the dactylus, are easily broken off. 



KET TO THE SPECIES OF THE GENUS DISSODACTYLTJS. 



A 1 . Dactyl of fourth ambulatory leg simple, not bifurcate. Carapace with no 

 more than one dorsal ridge on each side. Antero-lateral margin entire, 

 non-dentate. 

 B 1 . Carapace with a dorsal ridge on either side proceeding inward from the 



lateral angle. Legs not slender. 

 C 1 . Dorsal ridge oblique. 



D 1 . Secondary spine of dactyls of legs 1, 2, and 3 of good size. 

 E 1 . Dactyls of legs 1, 2, and 3 bifurcate half way to their base. 

 F 1 . Edge of front transverse. Carapace flat for the most part and 

 narrow, being only one-twelfth wider than long. 



nitidus, p. 116. 

 F*. Edge of front concave. Carapace very convex and wide, about 



one-fifth wider than long mcUitac, p. 117. 



E*. Dactyls of legs 1, 2, and 3 bifurcate less than halfway to their 



base , cncopci, p. 119. 



D*. Secondary spine of dactyls of legs 1, 2, and 3 minute and remote 



from primary spine borradailci, p. 121. 



C 1 . Dorsal ridge transverse stebbingi, p. 123. 



B 1 . Carapace without dorsal ridge. Legs slender a/coc/a, p. 124. 



A". Dactyl of fourth ambulatory leg bifurcate, as in the other pairs. Carapace 

 covered with numerous transverse ridges. Antero-lateral margin dentate. 



calmani, p. 125. 



