146 University of California Publications in Zoology  [VouL. 23 
Parapagurus mertensii (Brandt) 
Plate 16, figure 5 
Pagurus mertensti Brandt, in Middendorff, Reise in den dussersten Norden 
und Osten Sibiriens, Bd. II, Zool., Th. I, p. 112, 1851. 
Parapagurus mertensit Holmes, Occas. Papers Calif. Acad. Sci., 7, 155, 
1900; Rathbun, H. A. E., 10, 162, pl. 5, fig. 6, 1904. 
Characters —Median projection of front prominent, somewhat elongate, tip 
rounded, sides subparallel, lateral projections small; anterior portion of carapace 
about as wide as long. Eye-stalks short, about one-half length of anterior portion 
of carapace. Chelipeds pubescent, spiny, very unequal; right cheliped very large, 
carpus long, inner and outer margins spiny, convex upper surface armed with 
two rows of short spines, hand long, narrow, dorso-ventrally flattened, and bent 
inward at a slight angle to the carpus, rounded upper surface with small, sub- 
serially arranged granules which become more prominent on the fingers, inner 
and outer margins sharp, granulo-denticulate and parallel; left cheliped long, 
slender and attenuate, carpus subcylindrical, with three rows of spines on the 
upper surface, hand narrow, much longer than the carpus, palm very short, fingers 
long, narrow, and curved downward. Dactyls of ambulatory legs exceedingly long 
and slender, armed below with numerous spines. 
Dimensions.—Type: length of carapace 19.1 mm., width 14.8 mm. 
Type Locality—Kamchatka. 
Distribution —Kadiak Island, Alaska, to off San Nicolas Island, California, 
77 to 266 fathoms. 
Remarks.—This species affords one of those curious cases of commensalism with 
colonies of hydroids sometimes found among deep sea pagurids. The colony of 
hydroids covering the shell in which the crab lives forms a membranous growth 
which extends beyond the boundary of the shell and in course of time, according 
to Dr. Benedict, causes the shell to disappear, leaving its inhabitant with a mem- 
branous instead of a calcareous domicile. In the specimen which I have the 
covering is partly formed by the tip of a broken shell but mainly by an extension 
of the membranous growth formed by the colony of hydroids. This arrangement 
certainly affords the crab the advantage of allowing it to grow without having 
to undergo the troublesome experience of changing lodgings (Holmes). 
Family LirHopipaE 
Body erab-like. Abdomen more or less firm, in part at least; often segmented, 
bent under thorax; no tail-fan developed, uropods absent. Carapace quite firm 
all over. First pair of legs chelate; fourth pair like the third; fifth pair very 
small and folded under the carapace, making it appear superficially that the 
members of this family have but four pairs of legs, a character which easily 
distinguishes it from any other family of Decapods. 
KEY TO THE CALIFORNIA GENERA OF THE LITHODIDAE 
I. Abdomen soft, more or less loosely inflexed, unsegmented; at most only basal 
(second), and two terminal segments stiffened by thin calcareous plates; 
reinforcement of basal segment usually consisting of a pair of narrow 
marginal plates and a pair of lateral plates, between which there may be 
a median plate; abdomen occasionally armed with calcified granules or 
short spines. 
