THE TURBELLARIA 31 



ORDER 3. Polycladida, Lang ( = Cryptocoela, Oerst). 



Marine Turbellaria, in which the pharynx leads into a central enterori 

 which is produced laterally into a number of caeca that may branch and 

 extend nearly to the margin of the body. Typically this group is 

 digonoporous. 



The families may be arranged in two sections according to the presence 

 or absence of a ventral sucker (for anatomy, etc., see Lang, 42). 



SECTION A. Acotylea. Polycladida, without a sucker; with the mouth 

 central or post-central ; the genital pores being therefore near the hinder 

 end of the body. If tentacles are present, they are on the dorsal surface, 

 above the brain. 



FAMILY 1. PLAXOCERIDAE, Lang, with tentacles, central mouth, small 

 stomach ; penis directed backwards. Planocera, Blv. (Fig. XV. 1), 

 several species are pelagic (v. Gr.) ; P. inquilina, Wh., inhabits the 

 branchial chamber of the mollusc, Sijcotypus canaliculatus (64) ; Conoceros, 

 Lang ; Planknoplana, v. Gr. ; Stylochus, Ehrb. ; Stylochoplana, Stimp. ;, 

 Alloioplana, Plehn. ; Plagioplana, Plehn. FAMILY 2. LEPTOPLAXIDAE, 

 Stimpson, without tentacles ; intestinal caeca numerous. Discocoelis r 

 Ehrb., male and female organs open by a common pore ; Cryptocoelis, 

 Lang ; Leptoplana, Ehrb. (Fig. XV. 2, 3) ; Trigonoporus, Lang ; Acelis, 

 Plehn. ; Semonia, Plehn. ; Polyporus, Plehn. FAMILY 3. POLYPOSTIIDAE, 

 Bergendal (3), with several male copulatory organs. Cryptocoelidts, Berg. ; 

 Polypostia, Berg. FAMILY 4. CESTOPLAXIDAE, Lang, elongate, without 

 tentacles ; copulatory apparatus directed forwards ; Cestoplana, Lang ; 

 LatocestuSj Plehn. 



SECTION B. Cotylea. Polycladida, in which a sucker is developed 

 behind the genital pores ; mouth central or pre-central ; genital pores just 

 behind it. If tentacles are present, they are developed from the margin 

 of the body. 



FAMILY 5. ANOXYJIIDAE, Lang, with numerous penes arranged in a 

 row along each side, but with only one female pore ; mouth central ; 

 Anonymus, Lang (Fig. XV. 9). FAMILY 6. PSEUDOCERIDAE, Lang, 

 tentacles in the form of folds of the anterior margin of the body ; mouth 

 pre-central. Thysanozoon, Grube (Fig. XVI.) ; Pseudoceros, Lang ; Yungia, 

 Lang ; Thysanoplana, Plehn. FAMILY 7. EURYLEPTIDAE, Lang, mouth 

 pre-central ; pharynx tubular, directed forwards. Prostheceraeus, Schmarda ;. 

 Cycloporus, Lang ; one species is commensal with Polyelinid Ascidians ; 

 Eurylepta, Ehrb. ; Oligodadus, Lang ; Stylostomum, Lang ; Aceros, Lang ; 

 Amlhjceraeus, Plehn. FAMILY 8. EXANTIIDAE, v. Graff. Enantia, v. Gr. 

 (23), agrees in nearly all essential features with the Cotylea, but is without 

 a sucker (Fig. XV. 4, 5). FAMILY 9. PROSTHIOSTOMIDAE, Lang, body 

 narrow, elongated ; mouth far forwards ; tubular pharynx. Prosthiostomnm, 

 Quatref. (Fig. XV. 8). FAMILY 10. DIPLOPHARYXGEATIDAE, Plehn. Diplo- 

 pharynx, Plehn. 



Further Piemarks on the Polycladida. The Polyclads are 

 entirely marine ; some attain a considerable size, viz. six inches 

 or more; they are flat, more or less ovoid or leaf -shaped, 



