166 PROCEEDINGS OF THE ACADEMY OF [1888. 



May 1. 

 The President, Dr. Leidy, in the chair. ' 

 Twenty-six persons present. 



Parasites of the Rock Fish. — Dr. Leidy stated that he recently had 

 examined the gills and entrails of a Rock-fish, Lahrax lineatiis, 

 weighing 20 pounds, on which he made the following remarks. The 

 gills Avere swarming with the little crustacean parasite Ergasilus 

 labracis. In many of these the thorax and egg-sacs were opaque 

 milk-white, but in most of them the latter were more translucent 

 and of a blue color. This diiference is due to the devolopment of the 

 embryos, within which there appears blue pigment. 



Attached to the gills there were three opaque milk-white fluke- 

 worms and a fourth of the same kind was embedded in the muscular 

 coat of the pharynx. These appear to pertain to an undescribed 

 species, and may therefore be distinguished by the following name 

 and description : — 



DiSTOMUM gai.actosomum. Opaque milk-white, depressed, spat- 

 ulate, narrowest in advance, obtusely rounded at both extremities, 

 dorsally convex, ventrally flat. Head rounded truncate or trans- 

 versely oval discoid, with prominent margin, unarmed ; neck short, 

 slightly widening to the ventral acetabulum, which is sessile, larger 

 than the oral acetabulum, and with its orifice appearing triangular ; 

 posterior part of the body elliptical, in movement expanding and 

 becoming thinner and translucent, and concave beneath with 

 the opaque Avhite intestine on each side shining through. At rest 

 about 6 mm. long by 2 mm. wide ; elongating to 12 mm. by 2*5 mm. 

 wide posteriorly, and 1 mm. at the base of the neck. 



After being killed in dilute alcohol, the specimens remained of 

 spatulate shape, 6 to 8 mm. long, 2 mm. wide behind. The oral 

 acetabulum 0'625 broad ; the ventral acetabulum situated 1"375 

 mm. back of the summit of the head, was 0'875 broad. 



When the animal was in motion and expanded the posterior por- 

 tion of the body to such an extent as to render it translucent, the 

 intestine on each side became especially conspicuous through its 

 white opacity. The intestines extended directly from the minute 

 pharynx to the caudal extremity, more or less tortuous according to 

 the degree of elongation or shortening of the animal. They are 

 widest back of the ventral acetabulum and are sacculated. In the 

 expanded condition of the body, by transmitted light, it exhibited a 

 minutely reticular appearance, the lines of the rete being more opaque 

 white and apparently according with a capillary net communicating 

 laterally with the vessels proceeding from the caudal vesicle. The 

 opaque white appearance of the body seems to be due to the presence 

 of granules of calcium carbonate, for the application of acetic acid 

 caused their disappearance with the evolution of bubbles of gas, and 



