50 BULLETIN OF THE 



length. My specimens agree so throroughly with the description given by Von 

 Gralf that 1 have no hesitancy in classing them as Planocera pellucida. So great 

 a variability in size within a given species is not uncommon among the Turbel- 

 laria, and it is to be added that but few specimens of this species have been 

 captured as yet. 



Planocera •pellucida up to the present time has been recorded (Von Graff, loc. 

 cit.) from the Indian Ocean and from the North and South Atlantic, and with 

 Planocera gruhei and Stylochoplana sargassicola was considered by Von Graff as 

 one of the three known cosmopolitan Polyclads. The occurrence, then, of 

 Planocera pellucida in the North Pacific gives to this species the widest dis- 

 tribution of any pelagic Planarian. 



Stylochoplana californica, sp. nov. 



Figures 1, 3. 



One specimen, immature, marked, "Station 3435, surface " (26° 48' 0" N., 

 110° 45' 20" W., Gulf of California). Length 5 mm., breadth at widest point 

 2 mm., breadth opposite mouth 1.60 mm. Anterior end rounded, abruptly 

 expanded in the way characteristic of the genus, gradually tapering from the 

 constriction behind the expanded head portion to the blunt posterior extremity. 

 The indentation at the hind end shown in the figure is possibly the result of 

 some injury, although the margin in this region showed no evidence of it. 

 Color of the alcoholic specimen yellowish, very translucent. Margins of the 

 body smooth and even, showing no signs of folds or wrinkles. The most 

 striking character about the specimen is the conspicuousness of the nervous 

 system, which shows with remarkable distinctness, even in the uncleared alco- 

 holic condition, when viewed by transmitted light, it being possible to follow 

 the two posterior longitudinal nerve stems from the brain to the posterior end 

 of the body, where they unite with each other. Some of the transverse commis- 

 sures, as well as the finer ramifications of the cerebral branches, can also be dis- 

 tinctly traced for considerable distances. The posterior longitudinal stems 

 retain about the same diameter throughout their entire extent, uniting wath- 

 out diminishing in calibre. One stem becomes directly continuous with the 

 other, the two thus forming a loop at the posterior end of the body. The 

 nervous system may be said to consist of a closed ring, which gives ofiF 

 branches from its periphery, and is united by transverse commissures and bears a 

 bilobed enlargement at the anterior end constituting the brain. To my knowl- 

 edge such a condition of the nervous system exists only among Triclads {Pla- 

 naria limuW^). The eyes are arranged with striking symmetry both as regards 

 the tentacles and the roots of the cerebral nerves. The tentacular eye-spots 

 are larger than the cerebral ones, and there are five of them to each tentacle. 

 The symmetry would be perfect but for an additional pair of small cerebral 



1 L. von Graff, Kurze Mittheilungen iiber fortgesetzte Turbellarienstudien. 

 IT. Ueber Planaria liniuli. Zool. Anzeiger, Jahrg. IL, No. 26, pp. 202-205, 1870. 



