NO. 14 MANTER : DIGENETIC TREMATODES OF FISHES 365 



Opecoelus mexicanus, new species 

 (Plate36, figs. 36, 37) 



Hosts: Paranthias furcifer (Cuv. and Val.) 



Lutianus viridis (Val.) 

 Location : Ceca and intestine, once from the stomach 



Locah'ty: Clarion Island, Mexico. Here the trematodes were 

 found in 3 of 4 Paranthias and in 2 of 3 Lutianus. 

 They were not found in 9 Paranthias furcifer or in 

 3 Lutianus viridis from the Galapagos Islands. 



Number: Present in small numbers in the above-mentioned 

 infected hosts 



SPECIFIC DIAGNOSIS OF OPECOELUS MEXICANUS 

 Body flattened, elongate, tapering at each end, 0.935 to 1.957 in 

 length by 0.345 to 0.562 in greatest width. Oral sucker subcircular, 0.102 

 to 0.153 in diameter. Acetabulum about '^/^ body length from anterior 

 end, slightly wider than long, 0.189 to 0.255 in transverse diameter. 

 Sucker ratio approximately 3 :5. Aperture of acetabulum transverse, each 

 lip bearing 3 fairly long, pointed, median, fingerlike papillae and 2 lateral 

 rudimentary papillae, one on each side. Pharynx large, pyriform, elon- 

 gate, often widest in its anterior half, measuring 0.071 to 0.110 in length 

 by 0.053 to 0.085 in greatest width; esophagus varying according to con- 

 traction (from 0.020 to 0.068), when extended it is more than half phar- 

 ynx length ; intestinal bifurcation a short distance anterior to acetabulum ; 

 the narrow ceca extend to near posterior end of body where they unite to 

 form a short rectum; anus ventral, a little in front of posterior end of 

 body. Genital pore slightly to left of midline, opposite middle or the base 

 of pharynx. The small cirrus sac surrounds only the cylindrical cirrus and 

 a few gland cells. It reaches approximately to intestinal bifurcation. From 

 it a narrow male tube leads backward, gradually enlarging to form the 

 elongate, almost straight, seminal vesicle extending dorsal to the right 

 half of acetabulum and posterior to acetabulum a short distance. Testes 

 just posterior to midbody, tandem, close together, wider than long, 

 smooth, or slightly lobed; posttesticular space approximately Y^ body 

 length. 



Ovary immediately pretesticular, wider than long, somewhat heart 

 shaped (sometimes of irregular outline). Vitellaria extending lateral to 

 ceca from posterior edge of acetabulum to posterior end of bodj^, not meet- 

 ing posterior to anus; 2 longitudinal fields of follicles in posttesticular 

 space. In one specimen the anterior extent was almost to mid-acetabular 



