348 JULIAN D. CORRINGTON. 



Several varieties of Hyperid Amphipods and also certain small 

 fish are commonly known to seek shelter beneath the umbrella of 

 various medusae, but cases of large sized crabs occupying this 

 situation seem to be rare. No references in the literature involv- 

 ing either of these types of animal as commensals were found by 

 the writer, who is indebted to Dr. Mary J. Rathbun for the two 

 following citations : Rathbun, '04, in writing of the distribution 

 of Cancer jordani in Monterey Bay, California, notes " one under 

 rocks between low tide mark and mean tide, and three from the 

 subumbrella space of a large violet-and- white jellyfish " (specie? 

 not stated). Weymouth, '10, writes: "Cancer gracilis is repre- 

 sented by a considerable number of specimens, both young and 

 adult, all obtained by dredging, though in Puget Sound it is an 

 abundant shore crab. On several occasions the young of this 

 species has been found in considerable numbers clinging to the 

 subumbrella of various medusae. These have all been of small 

 size 5 to 10 mm. but it was not until the summer of 1908 that 

 younger stages were found. On one occasion a number of 

 medusae were collected and in examining these many very young 

 crabs were obtained and a smaller number of megalops. S^mr 

 of these were kept alive until the molt to the young crab stage 

 took place, so that there can be little doubt that the specimens were 

 really the megalops of gracilis. Later megalops were obtained 

 from other species of medusae, and crabs of a slightly larger size 

 than those found on the jellyfish were dredged in considerable 

 numbers ; it would appear, therefore, that in the case of gracilis, 

 at least a considerable number of individuals pass that portion of 

 their life history from the end of the free-swimming stage, prob- 

 ably early megalops, until reaching a size of 15 to 20 mm. clinging 

 to medusas, after which they drop to the bottom and live in the 

 manner of the adult. I have found no other species than gracilis 

 on medusae though Miss Rathbun reports one specimen of jordani 

 from the same situation. It would be interesting to know if this 

 form of life history were universal with gracilis and if it were 

 common in any other species." It will be noted that Weymouth 

 is incorrect in the number of specimens observed as commensal 

 by Dr. Rathbun, and also that no identifications of the medusae 

 involved are given. 



