56 PROCEEDINGS OF THE CALIFORNIA 



Second and third pairs of legs sub-equal, longer than the first, slender, 

 ending in a sharp claw; the third pair slightly longer than the second. 



Fourth pair immensely developed, exceeding in length the width of the 

 carapace, terminating in a stout claw. 



Fifth pair shortest, reaching to about the middle of the third joint of the 

 fourth pair; usually held in an elevated position over the posterior portion of 

 the carapace. 



Width of carapace a little less than % inch; length, ~% inch. 



Total length from claw to claw at fourth pair, % inch. 



Habitat, the sand-constructed tube of an annelid. 



I found this curious little crustacean on the tube of an annelid common on 

 the sandy flats left bare at low tide in Tomales Bay. While digging for those 

 sand-excavating lobsters, the Gebice and Callianassw, I found in abundance the 

 sandy tubes of an annelid about six inches long, with numerous joints or 

 nodes, each of which was surrounded by a circlet of seta3, by whose action 

 the creature propelled itself at pleasure up and down the tube. 



Believing the worm to be a new species, I gathered some, and while pulling 

 the tube to pieces, and admiring the rich brownish red tint conspicuous at 

 each node of my new prize, I was surprised to see a long narrow creature 

 move out, as I believed, head first; but a nearer inspection showed me that 

 the motion was sideways, and that the new-comer was no fourteen-legged 

 amphipod or isopod, but a true decapod crustacean. 



The short chelae, extremely lengthened fourth pair of legs, and short, broad 

 body, are so many adaptations to the mode of life of this creature, which 

 finds an ample dwelling-place in the space intervening between the body of 

 the annelid and the inside of the tube; up and down which it moves with its 

 long fourth pair stretched out in such a manner as to to give it the elongated 

 appearance of a Caprella, 



The width of Tubicola longipes from end to end of the fourth pair of legs is 

 eight times greater than its length from front to back. 



This is, so far as I am aware, the only instance known of a decapod crus- 

 tacean becoming the guest or commensal of an annelid, for although the 

 species of the family Pinnotheridce are all commensals, most of them reside 

 between the folds of the mantle of large bivalve mollusks, such as mussels 

 or clams (thus the Fab'm subquadrata lives within the mantle of Pach/desma 

 crassiteUoides, a large clam of this Coast), and a few live within the tests of 

 Echini, close to the anal aperture. 



It is most probable that this worm and its commensal may occur in many 

 other places besides Tomales Bay, possibly in San Francisco Bay, and I should 

 be much obliged if some of our friends who may go out on a fishing excursion 

 would bring me specimens, in alcohol, of the worm and its tubes, that I may 

 find whether the crab is its constant companion in all localities. 



The worm is one which is frequently used for bait. 



On April 20th, the females of this interesting little crustacean was loaded 

 with spawn. 



