300 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Platybothrium fip. 

 [Plate 42, fig9. 98, 99, TT. S. K M. No. 6527.] 



On August 18, a single specimen of the genus Platybothrium was obtained from the spiral valve 

 of the hammer-head shark (Sphyrna zygivna). As the genus with the previously-described species 

 { /'. cermnum) rests on a single specimen from the dusky shark (Carcliarinns obscnrus), I shall not 

 venture to bestow a specific name on this specimen until more material is available. 



The head agrees with /'. cervinum, particularly in the character of the hooks. There are, how- 

 ever, two cost;p on the posterior end of each bothrium, a character not clearly made out in P. ccrvinum. 

 The greatest difference is in the size; whereas the length of the specimen upon which the species 

 P. cerrinum was founded was 67 mm., that of the specimen under consideration is only 3.55 mm. The 

 neck in this specimen is densely beset with conical spines, which is not a character of the other. It is 

 possible that this may be a character peculiar to young strobiles. The difference in hosts can hardly 

 be considered as weighing against probable identity of species, as this specimen was associated with 

 several representatives of Phoreiobdflirium lasiiim, also first described from the dusky shark. 



Head as in P. cervhinm, broad, flat, and thin; bothria four, each armed with a pair of two- 

 pronged antler-like hooks, connected with each other at the base by a short chitinous bar; bothria 

 truncate in front, with two short costne behind. Neck spinose, slender, and of nearly uniform size for 

 about 0.7 mm., then enlarging abruptly, thickened and somewhat fleshy, probably a contraction con- 

 dition. Segments at first much broader than long, but increasing in length gradually; last segment 

 longer than broad, with rounded ends, not mature, but appeared to be loosely attached. 



Dimensions of living specimen in millimeters: Length 3.55, length of head 0.31, breadth of 

 head 0.35, diameter of neck 0.06, distance to first segment 0.48, length of first segment 0.1, breadth of 

 first segment 0.28, length of last segment 0.5, breadth of last segment 0.33, length of spines on neck 

 0.035, number of segments 6. 



The spines are abundant on the neck, becoming sparse on the first segments and occurring only 

 scatteringly on the lateral margins of other segments. 



Larval Cestode from the Bonito. 



[Plate 42, fig. 100, U. S. N. M. No. 6528.] 



Among the few entozoa found in the bonito (Sarda sarfla) is a small blastocyst which was 

 liberated from a cyst on the pyloric c;vca. The length of the living specimen was 3 to 6 mm., 

 depending on the state of contraction. When set free from the cyst it was very active, contracting 

 and expanding and oven making some headway in progression in a forward direction. There was a 

 small aperture at each end, and along the central region were numerous roundish bodies. There is a 

 well-marked constriction just back of the head in the alcoholic specimen, 0.13 mm. from the tip, 

 whence it tapers to a blunt point. The mouth communicates with a short canal. 



The following dimensions, in millimeters, are of the specimen mounted in balsam: Length about 

 4, breadth at anterior constriction 0.31, slightly broader than this a short way back of constriction, 

 then narrowing to 0.18 at middle, expanding again to 0.34 near the posterior end. 



Beginning just back of the constriction and continuing for about three-fourths of the length 

 there are suspended in the middle of the body an elongated cluster of pyriform structures, each about 

 0.035 in the longer and 0.028 in the shorter diameter. Each is attached by a slender stalk at the 

 smaller end. I have recorded something similar to this in a larval Rhynchobothrium from the 

 intestine of the sand shark (CarcJiarias littoralis). [Proceedings of the U. S. National Museum, vol. 

 xix, p. 797, pi. LXIII, figs. 14-16.] The walls of the body were very thickly set with nuclei. 



The specimen was embedded and cut into longitudinal sections in the attempt to ascertain the 

 nature of these pyriform bodies. Like the parenchyma generally they were scarcely at all stained by 

 carmine. By transmitted light they appeared to bo of a faint yellowish-brown color. No structure 

 could be made out in these central bodies. While many of them are pyriform, this designation does 

 not lit all of them. In sections the body wall is seen to be very thin. 



