NO. 14 MANTER : DIGENETIC TREMATODES OF FISHES 391 



mined). Genital pore median, imm.ediately preacetabular. Testes sub- 

 globular, not markedly longer than wide, of slightly irregular contour, 

 close together, intercecal, in posterior fourth of body. Cirrus sac almost 

 straight or bent at level of anterior end of seminal vesicle, extending from 

 ^ to ^ the distance from acetabulum to ovary; cirrus spined, extending 

 only slightly posterior to acetabulum; tubular genital atrium from pore 

 to near midacetabular level. Ovary globular, median, closely anterior to 

 anterior testis. Vitellaria from posterior end of cirrus sac to posterior end 

 of body; continuous; dorsal, ventral, and lateral to ceca (follicles may 

 not quite reach cirrus sac or may reach very slightly posterior to its pos- 

 terior edge) ; no follicles directly between gonads; metraterm spined, con- 

 siderably shorter than cirrus sac; eggs 60 to 71 by 32 to 42 fx. 



Comparisons. Only two other species of Stephanostomum show the 

 ventral interruption of the oral spines. These are S. bicoronatum (Stos- 

 sich) and S. cesticillum (Molin). S. megacephalum differs from both in 

 its much smaller size, less extensive anterior extent of the vitellaria, shape 

 of testes, smaller eggs, and shape of pharynx. 



The name megacephalum refers to the large oral sucker. 



Two specimens (figs. 71 and 74) of Stephanostomum from the same 

 host, one from San Francisco, Ecuador, the other from White Friars, 

 Mexico, were thought for a time to represent another species but are in- 

 cluded as S. megacephalum. They are only slightly larger (up to 3.307) ; 

 they have a sucker ratio of about 3 :2 rather than 5 :4 ; the testes are ovoid 

 and rather definitely longer than wide; the genital atrium is short; the 

 eggs 70 to 76 by 37 to 46 jx; and the oral spines are somewhat larger. 

 Other features such as number and arrangement of oral spines, location 

 of gonads, extent of vitellaria, and extent of cirrus sac are the same. Since 

 the degree of differences is small, it was decided that these specimens 

 could be considered as S. megacephalum. 



In a collection of Stephanostomum specimens from Caranx latus 

 Agassiz at Tortugas, Florida, one specimen, somewhat macerated and not 

 quite complete posteriorly, is identified as S. megacephalum. It agrees 

 with the Pacific material in sucker ratio, oral spines (there seem to be 

 only 30, but the count might be uncertain to that extent of difference, or 

 the median pair may have been lost), extent of vitellaria, extent and shape 

 of cirrus sac, egg size, and shape and position of the gonads. Other 

 Stephanostomum in the same collection belong to other species, one of 

 which is similar if not identical with the following species. These could 

 not be identified, however, with any certainty because of loss of spines, 

 unusual body extension, et cetera. 



