No. 4, — Reports on the Dredging Operations off the West Coast of 

 Central America to the Galapagos, to the West Coast of Mexico, 

 and in the Gulf of California, in Charge of Alexander Agassiz, 

 carried on by the IT. S. Fish Commission Steamer " Albatross," 

 during 1891, LiEUT, Commander Z. L. Tanner, U. S. N., 

 Commanding. 



[Published by Permission of Marshall McDonald, U. S. Fish Commissioner.] 



IX. 

 Report on the Turbellaria, Br "W. McM. Wood worth. 



The collection, although an extremely small one, is important from the 

 fact that it contains two species that are probably new, and shows for 

 one species, Planocera pellucida, a wider distribution than has heretofore 

 been known for it. Furthermore, it adds one to the number of species 

 of Polyclads that are known to be pelagic. Owing to the small num- 

 ber of specimens, I was unable to make sections of any of the material, 

 and my descriptions are based upon an examination of the specimens 

 cleared in glycerin. In such a comparatively superficial study an ac- 

 curate knowledge of the condition of the sexual organs, which is of great 

 systematic importance, could not be had. All of the forms belong to 

 the class Polycladida,^ and represent three genera. 



Planocera pellucida Mertens. 



Two specimens marked, " Surface, 8 P. M., 13° 33' 30" N., 97" 57' 30" W." 

 Only one specimen of the two was sexually mature, measuring 7 mm. in length 

 by 4.5 mm. broad. The other specimen exhibited no signs of the sexual glands, 

 only the penis and bursa being visible. A comparison of the material with a 

 description of this species recently given by Von Graff ^ leaves no doubt as to 

 their identity. The dimensions of the specimens measured by him are much 

 greater than those given here, his largest one being 18 mm. in length by 

 13 mm. across at the widest point, and another one measuring 14 mm. in 



^ L. von Graff, " Pelagisclie Polycladen," Zeitschr. f. wiss. Zool., Bd. LV. Heft 2, 

 pp. 189-2in, Taf VII.-X., 1892. Also in Arbeiten a. d. zool. Inst. z. Graz, Bd. V. 

 No. 1. 1892. 



VOL. XXV. — NO 4. 



