300 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Platybothrium Bp. 
[Plate 42, figs. 08, Ofl, IT. S.N. 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 zygoma). As the genus with the previously-described species 
(/’. cervinum) rests on a single specimen from the dusky shark ( Carcliarinus obscurus), I shall not 
venture to bestow a specific name on this specimen until more material is available. 
The head agrees with I\ cervinum, particularly in the character of tho hooks. There are, how- 
ever, two cost* on tho posterior end of each bothrium, a character not clearly made out in /'. cervinum. 
The greatest difference is in the size; whereas the length of the specimen upon which the species 
P. cervinum 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 Phoreiobolhrium lasium, also first described from the dusky shark. 
Head as in P. cervinum, broad, fiat, and thin; botliria 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 costm 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 nock 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. 
Tho 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 sarda) is a small blastocyst which was 
liberated from a cyst on the pyloric cmca. The length of tho living specimen was 3 to 6 mm., 
depending on the state of contraction. When set free from tho 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 tho 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 tho shorter diameter. Each is attached by a slender stalk at the 
smaller end. I have recorded something similar to this in a larval Rhynchobotlirium from the 
intestine of the sand shark ( Carcliarias littoralis). [Proceedings of the U. S. National Museum, vol. 
xix, p. 797, pi. iiXm, figs. 14-16.] The walls of tho 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. Liko tho 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 fit all of them. In sections the body wall is scon to bo very thin. 
