548 Dr. W. T. Caiman on an Epizoic Hydroid 



and invested by a delicate membranous perisarc. There is 

 no liydrocaulus, the polyps springing directly from the 

 liydrorhiza, the perisarc ot" which can with difficulty be seen 

 to be continued upwards for a very short distance at the base 

 of each. The largest polyps are about "5 mm. in height in 

 the preserved state, obconical in shape, expanding from a 

 narrow base to about "2 mm. in diameter at the distal end. 

 The tentacles are 10-12 in number, set in a single whorl, 

 surrounding a low convex hypostome. The branches of the 

 liydrorhiza are largely isolated, anastomosing here and there, 

 and only in one or two places showing a tendency to form a 

 closer network. 



In the characters of the hydrorhiza and of the sterile polyps 

 the species appears to approach most nearly to the genus 

 btylactis, Allman, which already includes several species of 

 similar epizoic habits, e. g., S. vermicola, Allman *, and 

 H. minoi, Alcock f (the latter more recently transferred to 

 Podocoryne by Stechow:):). From these and all the other 

 species hitherto referred to the genus the form now described 

 differs in the number of tentacles and in the low rounded form 

 of the hypostome. In view of the uncertainty as to its 

 generic position, however, it appears premature to distinguish 

 it by a specific name. 



The disposition o£ the hydroid colony on the surface of the 

 crab deserves further description. On the dorsal surface of 

 tiie carapace no polyps are developed, but the hydrorhiza 

 follows closely the inter-regional grooves, so that, when 

 viewed with tlie naked eye or with a lens of low power, most 

 of the regions appear to be sharply defined by a narrow line. 

 Tiie arrangement is not absolutely symmetrical, but it is 

 possible that in one or two places the hydrorhiza may be 

 imperfectly preserved. Each of the legs carries a single 

 trunk of hydrorhiza which runs along the merus just behind 

 its upper edge, apparently following, in the case of the walking- 

 legs, an ill-defined groove between the marginal row of spini- 

 form tubercles and a second row on the posterior face of the 

 segment. On the chelipeds this trunk spreads out in an 

 irregular fashion on the carpus, tending to form a network 

 of which the meshes are occupied by the granules of the 

 carpus ; the carpus bears two polyps of unequal size in 

 approximately corresponding positions on each of the cheli- 

 peds ; the hydrorhiza is continued along the upper edge of 



* Eep. Hydroida ' Cliallenger,' pt. ii. p. 2, pi. i. figs. 2, 2 a (1888). 

 t Ann. & Mag. Nat. Hist. (6) x. p. 207, fig. (1892). 

 t Zool. Anz. xxxii. p. 752 (1908) ; Abh. math.-phys. Kl. k. Bayer. 

 Akad. Wiss. i. SupiDl. Bd., Abh. (3, p. 17, pi. iv. fig. 8 (1909), 



