A, E. Verrill — 3farlne Planarians of Nexo England. 463 

 Stylochus zebra Verriii. 



Stijlochopsis zebra Verrill, Amer. Journ. Sci., vol. xxlv, p. 371, 1882; Annual 

 Report U. S. Com. of Fish and Fisheries, for 1882, p. 666,, 1884. 



Plate xl, figure 3 ; Plate xlii, figures 2, 2(i. 



Size large. Body thick and firm, when active oblong ov long- 

 elliptical, usually rounded at both ends ; in full extension often five 

 or six times as long as broad, but capable of contracting to a broad 

 oval or elliptical form. In full expansion the body is rather thin, 

 though convex doreally, but is nearly opaque, except at the margins, 

 which are translucent and often raoi-e or less undulated. In strong 

 contraction the body is convex, thick, and firm. Tentacles situated 

 not far from the anterior end, at about the anterior eighth or tenth, 

 and not far apart ; they are short, obtuse, white, filled with very 

 numerous, crowded, minute, black ocelli. Two large, rather open, 

 elongated cerebral clusters, composed of numerous very minute 

 ocelli, are situated between the tentacles and extend about the same 

 distance forward and back of them ; the hind ends of these clus- 

 ters are widest and contain the greatest number of crowded ocelli ; 

 the two clusters often blend, more or less, on the median line, and 

 terminate posteriorly rather abruptly. In some specimens these 

 clusters are imperfectly developed, with comparatively few ocelli ; 

 in others, of large size, additional scattered ocelli occur over the 

 whole anterior end, between the cerebral groups and the marginal 

 rows. The marginal ocelli are minute and very numerous ; around 

 the anterior end they form three or four irregular rows, but they 

 extend in one or two rows to the posterior end. The pharyx, as 

 contracted, is elongated and has five or six pairs of much divided 

 lobes anteriorly, and three or four pairs of successively smaller and 

 simpler lobes along the sides of the elongated posterior portion, 

 which ends not far from the middle of the body. Mouth anteriorly 

 situated about opposite the third pair of large stomach-branches and 

 pharyngeal lobes. There are, evidently, two genital pores, only a 

 short distance apart and inconspicuous.* The vas deferens extends 

 forward to about the posterior third of the stomach as a conspicuous 



*I have already stated, on a former page, that this is not a tjpical species Of 

 Stylochus, as that genus is defined by Lang, for it differs considerably from all the 

 European species iii the structure of the copiilatory organs, and especially in having 

 two separate genital openings. But our other species seem to agree with this in that 

 respect. It might be regarded, quite as well, as a Planocera ivith marijinal ocelli 

 and numerous tentacular ocelli. 



