3 6 4 



FRESH-WATER BIOLOGY 



is about one-half as wide as the pharynx and orbicular in outline. Apparently eyeless. 

 White. Length 4 mm., breadth 1.5 mm. Brooks, Carter Caves, Kentucky. 



Plagiostoma (?) planum Silliman 1885. 



Length 1.5 mm., breadth 0.7 mm. Mouth opening in anterior 

 end. Pharynx lies within a sheath and has both longitudinal 

 and transverse muscle layers. Radial muscle fibers pass from the 

 base of the pharynx to the body wall. Without eyes or other 

 sense organs. The poorly developed brain lies in front of the phar- 

 ynx as a transverse banq. The intestine is capacious and has short 

 lateral diverticula. This species probably belongs to the genus 

 Prorhynchus. 



FIG. 649. Plagiostoma (?) planum. ph, pharynx; d, intestine. X about 

 30. (After Silliman.) 



Acmostomum crenulatum Schmarda 1859. 



The body is cylindrical, yellowish, i mm. long. Pharynx cylindrical, protractile with six 

 deep lobes on its margin. Otolith large and spherical contained within a transparent capsule 

 which is located at the end of the first third of the body. 

 The ovaries form a large spherical mass in the posterior part 

 of the body. The cirrus is short knife-shaped and has a 

 slight double curve. Found in brackish water, Hoboken, N. J. 



FIG. 650. Acmostomum crenulatum. From life X about 30. 

 (After Schmarda.) 



Dendrocoelum sp. Pearl 1903. 



Agrees with description of Dendrocoelum lacteum, except in respect to the color. Color 

 ranges from a light grey to nearly black, and is uniform. Found about Ann Arbor, Mich. 



IMPORTANT REFERENCES ON NORTH AMERICAN FRESH- 

 WATER TURBELLARIA 



GRAFF, L. VON. 1882. Monographic der Turbellarien. I Rhabdocoelida. 



Leipzig. 

 1904-1912. Bronn's Klassen und Ordnungen des Tierreichs. IV. Bd., Wur- 



mer: Vermes, Turbellaria, Acoela, and Rhabdocoela. Leipzig. 

 1911. Acoela, Rhabdocoela und Alloeocoela des Ostens der Vereinigten 



Staaten von Amerika. Zeitschr. f. wiss. Zool., 99 1321-428. Taf. I- VI. 

 SILLIMAN, W. A. 1885. Beobachtungen iiber die Siisswasser-Turbelarien 



Nordamerikas. Zeitschr. f. wiss. Zool., 41 148-78; Taf. Ill, IV. 

 WOOD WORTH, W. McM. 1897. Contributions to the Morphology of the 



Turbellaria II. On some Turbellaria from Illinois. Bulletin Mus. Comp. 



Zool. Harvard Coll., 31 : 1-16; i plate. 



