no. 3638 TURBELLARIA — KAWAKATSU 15 



Of the four known North American species of the genus (D. piri- 

 formis, D. alaskensis, D. vaginatus, and D. hymanae) , only D. piriformis 

 is a pigmented form, with two eyes and a well-developed adhesive 

 organ. The Montana specimens of D. vaginatus are white and the Ore- 

 gon (vicinity of Portland) specimens of the same species are dark, but 

 microscopic examination shows that the dark color is caused by dark 

 points in the cells of the entoderm (Hyman, 1963). This species has 

 two eyes and an adhesive organ. Dendrocoelopsis alaskensis is also a 

 nonpigmented form but without an adhesive organ. This species has 

 two pairs of principal eyes. 



Dendrocoelopsis hymanae differs from the other members of the genus 

 in the following characters : moderate size, 14 mm in length (preserved), 

 white, and eyes wanting; adhesive organ more developed than in 

 D. vaginatus; testes prepharyngeal and ventral; penis bulb well devel- 

 oped; the seminal vesicle separated into two cavities (their positions 

 are somewhat asymmetrical in my specimen) and sperm ducts entering 

 separately; penis papilla conical, pointed, with single ejaculatory duct; 

 copulatory bursa large; bursal canal thickened but less developed 

 than in D. vaginatus) common ovo vitelline duct entering the roof of 

 the male antrum. 



Holotype. — One set of serial sagittal sections (No. 468a: 11 slides) 

 will be deposited in the Division of Worms, Museum of Natural 

 History, Smithsonian Institution; also one whole mount of the head 

 piece (No. 468b) and one set of sagittal sections of the posterior piece 

 of the same specimen (No. 468b: 2 slides). 



Locality. — Lake Tahoe, Station No. 23', at depths from 1554 to 

 1623 feet. 



Ecological Notes 



Lake Tahoe (fig. 1) is located in the Sierra Nevada Mountains at 

 an elevation of 2097 m. It is 35.4 km long, 19.3 km wide, has a 114-km 

 shoreline, a maximum depth of 548 m, and is the tenth deepest lake 

 in the world. Water temperature of the lake is — offshore surface: 

 maximum 20°C, minimum 5.5°C; at 67 m in depth: maximum 8°C, 

 minimum 5°C. 



Phagocata nivea tahoena and Dendrocoelopsis hymanae are the first 

 recorded true lake-dwelling planarians in the United States. The 

 former seems very common in the lake. Mr. Ted C. Frantz of the 

 Nevada Fish and Game Commission informed me (in litt.) that 

 "when we started our work on Tahoe we were surprised to find fairly 

 large concentrations of planarians at various locations. Particularly 

 so, when you consider Tahoe is relatively infertile. There has been 

 some speculation as to their feeding habits on lake trout eggs." I was 

 also much surprised to learn from the collector that a large number 



