390 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



ulum and both possess a very muscular cirrus sac and a tubular external 

 seminal vesicle. In Myzoxenus, however, the acetabular lips are lateral in 

 position rather than anterior and posterior. It might be noted that the two 

 species of Myzoxenus are both from related fishes in the Atlantic. M. 

 vitellosus Manter, 1934 is from Decodon puellaris and (in 2 of 14) 

 Calamus calamus. The other species of Myzoxenus (as yet undescribed) 

 is from Lachnolaimus 77iaximus. All of these genera of fishes with the 

 exception of Calamus are Labridae. 



AGANTHOCOLPIDAE Luhe, 1909 



Stephanostomum megacephalum, new species 

 (Plate41, figs. 71-74) 



Host: Caranx hippos (Linnaeus) 



Location: 6 specimens from the gills, one specimen from the 



intestine 

 Localities: Bahia Honda, Panama (type locality) 



San Francisco, Ecuador 



White Friars, Mexico 

 Number: 7 specimens from one host, one each from 2 others 



SPECIFIC DIAGNOSIS OF STEPHANOSTOMUM MEGACEPHALUM 



(Based on 7 specimens) 



Length 1.431 to 2.212; greatest width 0.375 to 0.465. Forebody Yz to 

 y^ total body length; posttesticular space % to i/io total body length. 

 Oral sucker 0.165 to 0.206 in diameter; acetabulum 0.165 to 0.195 in 

 diameter; sucker ratio varying from about equal to 5:4. Oral spines in 

 two rows, interrupted by a short space in midventral line; 30 to 32 in 

 number, almost always 32. The two pairs of spines immediately adjacent 

 to the midline space are smaller than the others, measuring 0.051 to 0.068 

 in length by 0.012 to 0.014 in width. The spines reach maximum size 

 laterally and dorsally, measuring 0.085 to 0.100 by 0.015 to 0.019. Im- 

 mediately posterior to the oral ring and opposite the oral sucker the skin 

 is free of spines. Body spines veiy large on forebody ; spination disappear- 

 ing a short distance posterior to acetabulum, the posterior half of body 

 apparently smooth. Prepharynx long; pharynx 0.187 to 0.262 in length 

 by 0.088 to 0.114 in width, subcylindrical rather than markedly pyri- 

 form; esophagus short. Prepharynx may be less than, equal to, or more 

 than pharynx length, according to state of contraction. Ceca ending close 

 to excretoiy vesicle with which they may connect (this point not deter- 



