64 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



side halfway from mid-line to lateral edge of body, inverted U- 

 shaped, left arm somewhat shorter than right and more slender, 

 posterior end of right arm bends on itself and after running anteri- 

 orly a short distance it bends back on itself and passes posteriorly 

 for a short distance. Oviduct arises from lower end of right arm. 

 No eggs present. 



Comparisons. P. ynexicana is very similar to P. trachuri Par. and 

 Per., 1890. The chief differences seem to be the more anterior posi- 

 tion of the genital pore which is near the pharynx in P. mexicana 

 but posterior to the intestinal bifurcation in P. trachuri; the apparent 

 lack of the anterior crown of genital spines; the more coiled vas 

 deferens and biloculate rather than uniloculate buccal suckers. The 

 vitellaria in P. trachuri extend forward to the genital pore and are 

 a considerable distance posterior to it in P. mexicana. P. trachuri 

 measures 4.0 to 6.0 mm. in length as compared to 1.95 in P. mexi- 

 cana which has, however, larger buccal suckers, larger suckers on 

 the haptor, and larger posterior hooks. The thirty-seven claspers on 

 the haptor are not significantly different from twenty-four to thirty- 

 two found in P. trachuri. 



P. mexicana is named after its geographic location, Mexico. 



Protomicrocotyle pacifica, new species 

 (Plate 9, figs. 64-74) 



Host: Xurel marginatus (Hill) 

 Location: Gills 



Locality: Port Culebra, Costa Rica 

 Number: 11 



Body elongate, flat, broadest at anterior third, attenuated an- 

 teriorly, and tapering posteriorly to the haptor, 2.8 to 4.33 mm. in 

 length, width at anterior third 0.996 to 1.430 mm. Posterior haptor 

 dumbbell-shaped bearing three pairs of hooks, outer hooks larger 

 and more anteriorly located, with sharp recurved points directed an- 

 teriorly and bifurcated enlargement at middle of length, 0.040 mm. 

 in length; second pair short, slightly anterior to inner pair, 0.016 

 mm. in length; inner hooks similar in shape to outer, 0.024 mm. in 

 length. Four posterior suckers on left side at posterior end, ventral, 

 elliptical, broader than long, 0.076 to 0.092 mm. in length by 0.108 

 to 0.120 mm. in width. Chitinous skeleton (fig. 65) consists of cen- 



