70 STALK-EYED CRUSTACEA. 
gitudinal depressions running the length of the segment; propodite long, 
closely set with piliferous squames on both surfaces; a longitudinal depres- 
sion runs from tbe articulation of the dactylus back to the carpus; both 
fingers densely pubescent within at base. Ambulatory appendages: meri 
rugose, with spinules on anterior margin, and a spine at the posterior angle 
of the distal end of the first and second pairs. The surface of the abdomen, 
sternum, and outer maxillipeds is thrown into setiferous folds or ridges. 
Color (in alcohol): reddish, lighter below, the pigment assuming the 
form of spots on the basal parts of the abdomen; a large blood-red spot 
on the propodite of the outer maxillipeds. 
Carapace, 5X 5 mm.; cheliped, 34 mm.; carpus, 10.5 mm.; chela, 20 mm. 
One male, taken with the preceding species on the reef at Panama at low 
tide, March 12. 
In the shape of the carapace and the front this species bears a close 
resemblance to Petrolisthes sexspinosus (Gibbes) and P. occidentahs Stimps., but 
the transverse ridges are more broken anteriorly, while posteriorly they 
extend uninterruptedly across the whole width of the carapace, being here 
more perfectly developed and less broken than in the two species named 
above. The carpus and claw, moreover, are longer and narrower, the ante- 
rior margin of the carpus is three-toothed instead of five-toothed. The 
squames of the carpus and claw do not tend to widen out into ridges or folds 
on either the upper or lower surfaces, but preserve the form of close set 
imbricated scales over the whole surface, including the space between the 
longitudinal depressions of the carpus and along the depressed line of the 
propodite. The form of the carpus approaches nearer to that of Petrolisthes 
armatus (Gibbes),* but the present species may be readily distinguished from 
P. armatus by the prominent ruge of the carapace, and squames of the che- 
lipeds. From P. edwardsii (Sauss.) the present species is distinguished 
by its longer chelipeds, by the ridges of the hinder part of the carapace 
extending clear across the carapace without interruption, ete. The ridges 
of the frontal lobes are much more strongly developed in P. agassizi than in 
any of the allied species mentioned above. 
* Porcellana armata Gibbes, Proc. Amer. Assoc. Adv. Sci., 3d Meeting, p. 190, 1850. Dr. Stimpson, 
when labelling the Crustacea in the Smithsonian Institution and Museum of Comparative Zodlogy, separated 
the Panama specimens of Petrolisthes armatus under the name of Petrolisthes similis, sp. noy., and specimens 
so labelled were afterward sent to the Jardin des Plantes, Paris. These were seen by Professor Henderson, 
and are referred to in his report on the “Challenger” Anomura, p. 109,as P. sémilis Stimps. But Stimpson, 
in publication, referred these specimens to P. armatus (Ann. Lye. Nat. Hist. N. Y., VII. 74, 1859), and 
never, so far as I can learn, published his P. similis. 
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