[135] NOTES ON ENTOZOA OF MARINE FISHES. 853 



I have had the opportunity of examining but two specimens of the 

 hammer-head shark (Sphyrna zygccna). These were obtained in different 

 years, and both yielded this parasite in abundance. The only other 

 parasites found in this host were a single Nematod in the spiral valve 

 of one, and a few cysts (Xenosites) in the muscular coats of the stomach 

 of each. 



Subfamily II. — Tetrabothriorhynchinse. 



Family Tetrabothriorhynchidw Dies. 



Tetrarhynchus Rudolphi. 



Bothriocephali spec. Bartels. 



Bhynchobothrii spec. Van Beneden and R. Leuckart. 



Tetrarliynclii spec. Van Beneden. 



Aspidorhynchus Molin. 



Tetrarhynchobothrium Dies. 



Body articulate, tseniaeform. Neck tubular. Head with four bothria 

 in two lateral pairs, parallel with the head. Proboscides four, termi- 

 nal, filiform, armed, retractile in the neck, free, i. e., not running through 

 the bothria. Genital apertures marginal or lateral. 



38. Tetrarhynchus tenue, sp. nov. 

 [Plate xiv. Figs. 5,6.] 



Head variable, but often sagittate. Bothria four, in two lateral pairs, 

 long-oval, long-elliptical, or oblong. Proboscides four, somewhat quad- 

 rangular, a little shorter than the bothria, densely beset with very slen- 

 der straightish or slightly arcuate spine-like hooklets, which are of nearly 

 uniform size and shape. The proboscides emerge from a point a short 

 distance back of the apex of the head. Neck tubular, contractile. In 

 life 4 it may be twice as long as the bothria, but in alcoholic specimens 

 it is usually shorter than the bothria. Posteriorly it is continued in a 

 collar which incloses the anterior part of the body. It is ordinarily 

 broader than the anterior part of the body. The proboscis sheaths are 

 nearly straight, with the exception of a single spiral kink in front of 

 the contractile bulbs. The latter organs are short-oval — in alcoholic 

 specimens less than one-third the length of the bothria. The segments 

 begin immediately behind the neck as fine transverse wrinkles. The 

 first distinct segments are very short, subsequently increasing in length, 

 becoming squarish, then longer than broad. The posterior mature seg- 

 ments are considerably longer than broad, with a tendency, in alcoholic 

 specimens, to become convex on the margins, thus giving a decidedly 

 repand outline to the margins of the mature portions of the strobile. 



Genital apertures : male, marginal, a little in front of the middle point. 

 Cirrus rather short and smooth ; female aperture lateral (?). Ova small, 

 spheroidal, escaping from lateral aperture. General habit of body more 

 slender, especially head and anterior part of body, than T. robustum. 



