40 PROCEEDINGS OF THE NATIONAL MUSEUM vol.81 



DIOCH'ETOS, new genus 



Geneiic diagnosis. — Linstowinae: With relatively few elongate 

 segments. Mature segments two to six times as long as broad. Geni- 

 tal pores alternate irregularly, and the sexual ducts pass dorsal to 

 the single lateral excretory duct. The dorsal excretory ducts and 

 secondary ramifications are usually absent except at the extremities 

 of young worms. Testes very numerous with a tendency to arrange- 

 ment in two lateral fields. Ovary median and very small. About 

 the anterior two-fifths of a mature segment is unoccupied by the 

 sex glands. Uterus breaks up into capsules, each of which contains 

 a single egg. The capsules are evenly distributed but very sparse. 

 Adults parasitic in lizards of the genus Phrynosoma. The above 

 diagnosis is based on a single species, and will doubtlessly have to 

 be modified if other species are discovered. 



Type species. — Diochetos phrynosomatis, new species. 



DIOCHETOS PHRYNOSOMATIS, new species 



Plate 3, Figure 7 ; Plate 4, Figure 1 



Spedftc diagnosis. — Diochetos: A flat white tapeworm, composed 

 of relatively few elongate segments. The total length varies from 

 55 to 70 mm. The scolex is 0.4 to 0.6 mm wide, and the suckers are 

 only 0.145 to 0.16 mm in diameter. There is no line of demarcation 

 between the neck and the scolex. Segmentation becomes apparent 

 about 2 mm from the scolex ; and almost immediately the rudiments 

 of the sex organs appear. The mature segments are 15 or 20 mm 

 from the scolex. They vary considerably in length but are always 

 much longer than broad. In my material, segments in which the 

 uterus has not yet developed may be as much as six times as long 

 as broad; younger segments, which seem to be perfectly mature, are 

 not quite three times as long as broad. Extreme measurements are 

 1 by 6.1 mm for the older segments and 1 by 2.45 mm for the younger. 

 The genital pore lies between the end of the first fifth and the end of 

 the first third of the lateral margin. The cirrus sac is an oval meas- 

 uring from 0.13 by 0.22 mm to 0.18 by 0.3 mm. The vas deferens 

 lies directly posterior to the median end of the cirrus sac. It is at 

 first much coiled, but straightens before reaching the level of the 

 ovary. There are 125 to 180 testes in each segment. These lie almost 

 wholly posterior to the ovary, but in nearly every segment a few lie 

 cephalic to that organ. They tend to group themselves in two elon- 

 gate lateral fields. The ovary lies slightly anterior to the center of 

 the segment. It is bilobed and relatively small, about 0.25 mm wide. 

 Behind it lie the vitellaria and shell gland in the usual positions. 



