PUGET SOUND CRUSTACEA. 283 



RHIZOCEPHALA. 

 Sylon sp. 



A single specimen of a RJiizocepJialan, probably referable to 

 this genus, was in the collections sent me, and I understand 

 that further specimens were obtained. In Messrs. Harrington 

 and Griffin's paper on the Puget Sound Invertebrates (Trans. 

 N. Y. Acad. Sci., 1897, p. 164) a" Sacciilina'' is recorded as 

 occurring on Scla^ocrangon iminitiis (Dana). From a sketch 

 kindly sent me by Mr. Harrington I gather that a specimen 

 occurred on a Pandahis Dance Stimpson. In the specimen sent 

 to me, only the abdomen of the host is preserved and this is 

 certainly not that of a Pandahis nor of a Sclcrocrangon^ but ap- 

 parently belongs to some species of Hippolytc. 



The parasite is attached as usual to the under surface of the 

 third abdominal segment of its host. It has an ellipsoid shape, 

 the longest axis lying nearly parallel to the longitudinal axis of 

 the host's body and measuring about 4 mm. Transversely to 

 the body of the host the parasite has a diameter of 3.4 mm. and 

 its vertical depth is 3 mm. The base of attachment is about 2 

 mm. in diameter and somewhat nearer the posterior pole. The 

 genital openings could not be detected (Hoek states, in his ap- 

 pendix to the Challenger Report on the Macrura, p. 923, that 

 these openings are closed in young specimens), nor was any 

 trace of the mesenteric Hne visible. The branched '''roots " are 

 easily visible inside the body of the host. Hoek states (lb., p. 

 924) that in Sylon, contrary to what obtains in Sacctdina, the 

 roots do not reach the intestine of the host, but are, for the most 

 part, confined to the space between the ventral muscles of the 

 abdomen and the integument. In our specimen, however, the 

 roots penetrate further into the body and form a plexus sur- 

 rounding the intestine. 



