POLYCLAD FLATWORMS — HYMAN 587 



wards from it on each side occur the coils of the two uteri, filled with 

 large eggs. The male copulatory apparatus underlies the left side 

 of the pharynx and the male gonopore lies at the anterior margin 

 of the pharyngeal cavity (fig. 16a). At the posterior end of this 

 cavity coils of the spermiducal vesicles can be seen approaching the 

 proximal end of the long fusiform seminal vesicle which is nearly as 

 long as the pharynx in the specunen, underlying the left side of this 

 organ. The seminal vesicle is provided with a coat of circular muscle 

 fibers and is filled with a dense mass of sperm. At its distal end the 

 seminal vesicle narrows to a duct that underlies the oval prostatic 

 vesicle, in which the radiations of the glandular interior are clearly 

 visible. At the distal end of the prostatic vesicle is seen the short 

 penis stylet with truncate tip. Other details are not discernible in 

 the whole specimen. The fact that the male apparatus lies under 

 the posterior half of the pharynx in the medium sized specimen (fig. 

 156) is rather puzzling and seems to indicate a forward migration of 

 this apparatus with sexual maturity. 



Differential diagnosis: Acerolisa rvgosa is distinguished by the 

 rugose dorsal surface, anterior position of the male gonopore, and 

 short truncate penis stylet. Of other species with a similar anterior 

 position of the male gonopore, A. inconspicua (Lang) (1884) has very 

 few eyes, A. meridiana (Ritter-Zahony) (1907) has the intestinal 

 branches anastomosed to a network, and A. californica HjTnan 

 (1953a) has a long pointed penis stylet. 



Holotype: USNM 28662, whole mount. The other five specimens 

 (USNM 28663-USNM 28667) are also whole mounts. 



Remarks: Marcus (1947) listed and gave characters of the seven 

 valid species of Acerolisa known at that time. In the same article he 

 described three new species of Acerolisa: piscatoria, leuca, and bituna. 

 Since then there have been named: A. arclica Hyman (1953a), cali- 

 fornica Hyman (1953a), and mullicelis Hyman (1955a). Mention 

 should also be made of Oligocladus albus Freeman (1933), which prob- 

 ably belongs to Acerolisa, but the one specimen is so imperfectly known 

 that decision is impossible at present. 



Family Prosthiostomidae 



Prosthiostomuni exiguum, new species 



Figures 166,c; 17a 



Material: Two specimens were taken by D. Reish on Eniwetok 

 Atoll, on coral rock on the inner reef flat, Sta. E-8, Aug. 21, 1956. 

 A third specimen, taken in the same locality and type of habitat at 

 Sta. E-2, was so distorted and broken that it was discarded as useless. 



General characters: This is a very small species, with the two 



