490 PROCEEDINGS OF THE NATIONAL MUSEUM vol.89 



Reproductive system. — Specimen fully mature but reproductive 

 system much damaged ; center of specimen filled with a mass of eggs, 

 apparently from ruptured uteri; periphery showed numerous testes 

 (fig. 31, d) . Beneath and behind pharynx male copulatory appara- 

 tus could be seen in whole mount; sections showed it to be typical 

 of the genus Acerotisa, but stylet, male antrum, and penis slieath 

 were missing. Penis below pharynx; penis papilla elongated; free 

 prostatic vesicle of oval form with moderately muscular wall ; coiled 

 mass of vasa deferentia could be seen around proximal end of sem- 

 inal vesicle. Nothing of the female apparatus was discernible except 

 a dense cloud of cement glands shortly behind the penis. 



Differential diagnosis. — Size, number of eyes in eye clusters, and 

 tubular seminal vesicle serve to distinguish this species. 



Distribution. — St. Josephs Bay, Fla. 



Tyj)e.— One set of serial sections (2 slides), U.S.N.M. No. 20535. 



Remarks. — The lack of tentacles, eye arrangement, and euryleptid 

 male apparatus leave no doubt that this species belongs to the genus 

 Acerotisa, despite the imperfect condition of the specimen. Bock 

 (1922) has pointed out that cerebral clusters composed of just two 

 large eyes (with or without accompanying small eyes) occur in sev- 

 eral cotylean genera {Stylostoniu/ni, Acerotisa, Chromoplofna) and are 

 also characteristic of young pseudocerids, so that they are probably 

 of ancestral significance. In the genus Acerotisa such cerebral 

 clusters are known for A. inconspicuus (Lang, 1884), A. notmlata 

 (Bosc, 1801) (for description see Hyman 1939b), and the present 

 species. 



Family PROSTHIOSTOMIDAE Lang, 1884 



Definition. — Cotylea of elongate slender form, without tentacles; 

 pharynx in anterior body half, long and tubular, directed forward, 

 mouth at anterior end of pharynx, just behind brain ; with a band of 

 eyes along the anterior margin, paired cerebral clusters also present; 

 male copulatory apparatus with two spherical accessory vesicles; 

 penis with a stylet. 



Genus PROSTHIOSTOMUM Quatrefages, 1845 

 Definition. — ^With the characters of the family. 



PROSTHIOSTOMUM LOBATUM Pearse, 1938 



Prosthiostomum lobatum Pearse, 1938, p. 91, fig. 34. 



Material. — Many whole mounts labeled Prosthi^stommn lohatimh; 

 set of serial sections made from one of these. 



Form. — Slender, elongated, anterior end rounded, posterior end 

 obtusely pointed ; maximum lengtli 17 mm., width 2.7 mm. (measured 

 alive by Pearse). 



