No. 5 meserve: monogenetic trematodes 65 



tral piece slightly broader at base bifurcating at distal end; one 

 pair of lateral pieces connected posteriorly with blunt tip at distal 

 ends and a pair of projecting pieces, stout and bluntly pointed, 

 pointing halfway to base of sucker and obliquely toward central 

 piece; one pair of lateral pieces separated posteriorly, not as long 

 as other pair. Brain anterior to pharynx. No eyes. Excretory pores 

 paired, dorsal, lateral almost to the edge of worm. Mouth sub- 

 terminal, ventral. Two anterior suckers elliptical, without mem- 

 branous septa, broader than long, 0.044 to 0.054 mm. in length, 

 0.060 to 0.092 mm. in width. Pharynx longer than wide, bulb-shaped, 

 0.100 to 0.116 mm. in length by 0.080 mm. in width. Esophagus 

 long, branched, in mid-line to right of genital atrium and to left of 

 vaginal opening, bifurcating short distance posterior to genital open- 

 ing. Intestinal crura extend to haptor, separated posteriorly, numer- 

 ous lateral branches to outside, few to inside. Genital pore ventral, 

 to left of mid-line. Genital atrium elliptical, large, longer than broad, 

 with ten short hooks and ten long hooks with sharp recurved points, 

 short hooks 0.108 to 0.120 mm. in length, long hooks 0.168 to 0.184 

 mm. in length. Ovary in posterior part of body. Genitointestinal 

 canal present. Vitellaria, fine, acinous, extend from genital atrium 

 to haptor, separated in front and intermingled behind. Uterus opens 

 into side of genital atrium. Vaginal opening ventral, to right of mid- 

 line, armed with numerous, short, triangular spines, 0.008 to 0.012 

 mm. in length. Vagina simple. Testes anterior to ovary, small and 

 numerous (150 to 200). Vas deferens opens into base of genital 

 atrium. Cirrus muscular, unarmed, cylindrical, in genital atrium. 

 Eggs 0.046 mm. in width by 0.160 mm. in length with polar fila- 

 ment at each end. 



Comparisons. P. mirabile (MacCallum) from Caranx hippos 

 differs from P. pacifica in the length of the genital atrium spines, 

 measuring 0.040 mm. in length and all approximately the same 

 length, compared to spines of P. pacifica of two sizes, three to four 

 times the length of spines of P. mirabile. The eggs of P. pacifica are 

 0.046 mm. in width by 0.160 mm. in length compared to 0.320 to 

 0.720 mm. by 0.080 to 0.140 mm. 



Discussion. This is another example of related species living on 

 related hosts among the ectoparasitic trematodes. The type species, 

 Protomicrocotyle mirabile (MacCallum, 1918), was found on Caranx 

 hippos Linnaeus from the New York Aquarium. The above species, 



