AitT. 21. PARASITES OF SHAEKS AND SKATES ^LINTON. 41 



THYSANOCEPHALUM THYSANOCEPHALUM (Linton). 



Phjillobothrium thysanoceph alum. 



1SS96, pp. 464-^68, pi. 2, figs. 1-12. 



Tliysaiioceithalum crispnm. 



1890, pp. 823-824. 



1801 &. 



18970, p. 448. 



1907e, pp. 113, 116. 



190S?>, pp 162-163, 165, 174-175. 



1910c, pp. 693-694. 



1911, p. 589. 



This cestode has been recorded hitherto only from the tiger shark 

 {Galeocerdo arcticus), in which it has been found to be invariably 

 present in the spiral valve, in large numbers, both young and mature 

 strobiles, and large numbers of free, ripe proglottides. 



Below will be found records of this cestode from a new host, tlie 

 hammerhead shark ( Cestracion zygaena) . 



Record of finds of this cestode not before published. Collections 

 on the two 1908 dates were made in Tortugas, others at Woods Hole. 

 Galeocerdo arcticus. 



1905, August 26 : Large numbers in spiral valve, adult to very 

 small, with intermediate sizes, and many free proglottides ; approxi- 

 mately 180, of which 80 were adult. 



1907, August 7: 1 large specimen in stomach; 15 large, 13 medium, 

 and 30 small specimens in spiral valve, with large numbers of free 

 proglottides; largest 420 mm. in length. 



1908, June 14 : 200, approximately, small and medium. The spiral 

 valve had been preserved in formalin at the Tortugas laboratory, 

 and was examined by me on June 27. The shark had not been iden- 

 tified, but the character of the spiral valve, and the presence of large 

 numbers of this cestode point to this host. June 24: Numerous, 

 small and large, with free proglottides; from a shark 370 centime- 

 ters in length, Tortugas. The shark was taken before my arrival 

 at the laboratory ; the spiral valve had not been preserved, but some 

 of the cestodes had been kept in formalin. 



1910, September 3 : 41, adult and young, longest about 220 mm. ; 

 one small specimen noted with forked posterior end. The gelatinous 

 tissue plug, described in a former paper (1900, p. 271, fig. 102) as 

 a tumor, is evidently normal, and is a structure whose function seems 

 to be to prevent, or to render difficult, the passage of undigested 

 pieces of food through the pylorus. 



1912, August 19 : 59 large, 494 medium and small, and large num- 

 bers of free, ripe proglottides, in spiral valve; maximum length 

 about 600 mm. ; from a 180 centimeter shark. 



