S. Yoshida 
571 
4. Acanthobothrium coronatum (Rud., 1819) van Beneden, 1849. 
Syn. Bothriocephalus coronatus Rudolphi, 1819. 
B. bifurcatus Leuckart, 1819. 
Tetrabothrius coronatum (Rud., 1819) Wagener, 1854. 
Calliobothrium coronatum (Rud., 1819) Diesing, 1863. 
C. corollatum (Abildg., 1790) Mont., 1887 of Beauchamp, 1905. 
The specimens were obtained from the spiral valve of Dasyatis 
akaei (Muller and Henle) on 5. iv. 1913, in Nakatsu, West Japan. 
They are very abundant and almost all of equal length (200 mm.). 
This is apparently identical with the well-known species A. coronatum 
(Rud., 1819) van Beneden, but my specimens differ somewhat from 
the descriptions thereof by the several authors. I shall describe these 
differences and my observations on this worm. 
External characters. Dimensions of various parts of worm, 
fixed by formalin, are as follows (in mm.): 
let Post. Last 
Head Hook Neck segment segment segment 
Length 1-0 0-18—0-19 80—100 0-1 0-3 0-5—0-6 
Breadth 1-2 003 0-46—0-6 0-75 1-3—1-6 1-3—1-5 
The scolex or head is subquadrate, broadening slightly behind. 
The bothridia are four in number, opposite one another, and of charac¬ 
teristic elongated oval form; each bothridium is divided into three 
unequal loculi by two transverse costae, the anterior loculus is the 
largest and deep, the posterior one the smallest and shallow; the 
bothridium is provided with a pair of bifurcated chitinous hooks at 
the anterior corner of the first loculus. The hook measures 0-18— 
0-19 mm. in length from base of the common stalk to the tip of prong; 
the basal common stalk is shorter than any of the prongs; the inner 
prong is a Httle shorter than the outer one; the base of the prong 
measures 0-03 mm. in diameter. In front of each pair of hooks there 
is the single accessory sucker, which is more or less muscular and deep. 
The neck is widest just behind the head, being nearly as wide as 
the posterior part of the head; it gradually narrows toward the middle, 
where it is narrowest, then widens gradually toward the first segment. 
In my specimens the neck is fairly long, as shown in the above table; 
this may be due to their preservation in an extended state. All 
previous authors describe the neck as short. The neck merges insen¬ 
sibly into the strobila, the anterior segmentation being very obscure 
