NO. 14 MANTER: DIGENETIC TREMATODES OF FISHES 399 



Dihemistephanus brachyderus, new species 

 (Plate43, figs. 83-86) 



Hosts : OligopUtes saiirus ( Bloch and Schneider) 



Caranx hippos (Linn.) ? 

 Location: Intestine 

 Locality: San Francisco, Ecuador 



Number: 8 specimens from 2 O. saurus; one specimen from C. 

 hippos. In C. hippos it occurred with Stephanosto- 

 mutn longisomuTTi and S. megacephaliiin 



The genus Dihemistephanus was named by Looss in 1901. It is dis- 

 tinguished from the genus Stephanostomum chiefly because the oral 

 spines are interrupted by a wide ventral space. The genus was more com- 

 pletely described by Little in 1930. Only 2 species are known to date: 

 S. lydiae (Stoss.) Looss, the type, and S. sturionis Little. 



There is some doubt that the present species belongs in Dihemi- 

 stephanus rather than in a new genus. Divergences shown are the ten- 

 dency for a dorsal as well as a ventral break in the rows of oral spines, the 

 complicated folds of the oral sucker, and the thick-walled, convoluted ex- 

 cretory tubules. However, it seems evident that the dorsal break in the 

 oral spines and also the shape of the oral sucker are variable characters. 



SPECIFIC DIAGNOSIS OF DIHEMISTEPHANUS BRACHYDERUS 

 Length 2.632 to 6.480; width 0.315 to 0.652. Forebody 0.217 to 

 0.292, usually about %o body length but in one case about Vjo body 

 length. Pigment flecks in forebody. Fine scalelike spines cover body as far 

 back as ovary but are lacking on ventral surface of forebody. Oral sucker 

 0.120 to 0.262 in transverse diameter; acetabulum 0.150 to 0.285 in 

 transverse diameter. The transverse diameters of the suckers may be 

 equal, or the acetabulum may be slightly larger. Acetabulum always 

 longer than wide, usually considerably so, ratio of width to length about 

 3 :4. Acetabulum usually tapering posteriorly ; somewhat protuberant and 

 overlapping forebody. Oral sucker with crown of narrow spines alternat- 

 ing so closely that the shorter posterior row often seems to lie directly 

 beneath anterior row ; separated by a wide ventral space and usually by a 

 shorter dorsal space. Spines, however, rather easily lost ; number of spines 

 about 50 to 60; smallest spines (ventral) about 20 to 27 by 5 to 6 //.; 

 largest spines (lateral) about 60 by 7 to 8 /x. Oral sucker with small 

 longitudinal aperture, an anterior sometimes protuberant cone-shaped 

 lobe, ventrolateral lobes, and two wider and thicker dorsolateral lobes 

 (figs. 84 and 85). The appearance is usually that of an inner portion 

 more or less pulled down into an outer portion (fig. 86 shows sections cut 



