NO. 14 MANTER : DIGENETIC TREMATODES OF FISHES 425 



into narrow part of body. Vas deferens, without gland cells, veiy long 

 and straight, extending entire length of narrow part of body (1.2 to 3) 

 to near sinus sac; near its anterior end it is again surrounded by gland 

 cells forming a second pars prostatica. Or, expressed differently, the pars 

 prostatica and prostate gland are divided into two parts by a very long 

 vas deferens. Sinus sac muscular but thin walled, subcylindrical, preace- 

 tabular; genital atrium lacking or very small. 



Ovary median, kidney shaped, transversely extended, immediately 

 posterior to testes. Mehlis' gland at its posterior border. Seminal recep- 

 tacle large, dorsal and posterior to Mehlis' gland. Laurer's canal lacking. 

 Vitelline glands in the form of long coiled tubes, 4 on one side, 3 on the 

 other; chiefly lateral but partly ventral; extending in middle half of 

 widened part of body. Uterus coiling backward into ecsoma, then for- 

 ward; coils in widened body chiefly lateral, extending between vitellaria; 

 coils gradually straighten along left side of seminal vesicle; uterus narrow 

 and straight throughout the long narrow part of body, entering base of 

 sinus sac; metraterm not differentiated. Eggs thin shelled, ovoid, 17 by 

 8.5 to 10 fi. Excretory vesicle forking anterior to testes; branches uniting 

 dorsal to pharynx. 



The name mecoderus is from meco (= long) and derus (= neck). 

 The name oligoplitis is for the host. 



GENERIC DIAGNOSIS OF MECODERUS 



Fairly large Hemiuridae with ecsoma, without cuticular denticula- 

 tions. Body much elongated with narrow, flattened anterior necklike re- 

 gion and a shorter, widened, plump posterior region containing reproduc- 

 tive organs and ecsoma. Suckers large, close together, distant from re- 

 productive organs. Seminal vesicle a simple thin-walled sac. Prostatic 

 portion of duct divided into a rather short, coiled pars prostatica near the 

 testes and a shorter pars prostatica near the sinus sac, these two regions 

 separated by a very long vas deferens. Vitelline glands tubular and coiled. 

 Seminal receptacle large ; Laurer's canal lacking. Sinus sac preacetabular, 

 simple, rather small and weak. Crura of excretory vesicle uniting dorsal 

 to pharynx. Type species : Mecoderus oligoplitis. 



Comparisons. This hemiurid is unusual in its peculiar body form and 

 in the long stretch of the vas deferens between the testes and the sinus sac. 

 The lobed posterior border of the mouth is also peculiar. The trematode 

 is to be compared to other smooth, tailed forms with tubular vitellaria 

 (i.e., Stomachicola Yamaguti, 1934; Erilepturus Woolcock, 1935; and 



