60 REPORT ON THE TUNICATA OP PLYMOUTH. 



Plate II, fig. 6, in a drawing taken from preserved material. These 

 structures are seen to have a flattened triangular shape and are 

 connected at their bases by very low and rudimentary horizontal 

 membranes (cf. fig. 7). In life, these papilla assume a more ex- 

 tended digitiform shape, as Lister long ago stated. If these papillae 

 were to be counected by internal longitudinal bars (as frequently 

 occurs in the Naples species), meshes would be formed, each con- 

 taining two stigmata. 



The opening of the duct of the hypoganglionic gland (fig. 7, c. v.) 

 is simply circular. It is situated in front of a raised triangular 

 area, whose apex is posterior ; this constitutes what is undoubtedly 

 the homologue of the epipharyngeal groove. A precisely similar 

 structure has been figured by Roule for Rhopalsea nepolitana,^ and 

 observed in Sluiteria ruhricollis by E. van Benedeu.f From the 

 posterior apex of this area arises the dorsal lamina (fig. 7, d. I.) as 

 a low membrane which increases slightly in height as it extends 

 posteriorly. At the level of each horizontal membrane it rises up 

 into a curved triangular languette (1), and occasionally there is a 

 small projection from its edge between each pair of interserial 

 languettes (fig. 8, i. p.). An examination of fig. 7 also shows that 

 the horizontal membranes really are continued upon the lateral 

 faces of the dorsal lamina, although they do not extend along the 

 languettes. 



The structure of the dorsal lamina in this species approaches 

 closely in essential features that described by van Beneden in 

 Sluiteria ruhricollis, in which form there is a continuous longitudinal 

 membrane whose border is cut into festoons in correspondence with 

 the number of transverse (interserial) bars. The lamina is provided 

 with fourteen oblique ridges which also correspond in number with 

 the horizontal bars. Although in his diagnosis of the genus 

 Sluiteria, Professor van Beneden denies the presence of horizontal 

 membranes {I. c, p. 43), he admits in his description of S. ruhricollis 

 that the connecting ducts of the internal longitudinal bars " spring 

 by an enlarged base from little interserial folds traversing the length 

 of the transverse bars " (p. 34). This is precisely the condition I 

 have found in the Naples Perophora, and it is essentially similar to 

 what is here described for P. List&ri ; interserial membranes are in 

 each case present, but rudimentary. The ridges on the lamina of 

 S. ruhricollis are therefore undoubtedly of the same nature as the 

 less conspicuous elevations formed in P. Listeri by the continuation 

 of the horizontal membranes upon the sides of the lamina (see fig. 7). 



* Roule, Eev. des Esp. de Phallusiad^es de Provence, Rec. Zool. Suisse, iii, pi. xiv, 

 fig. 14. 



t Ed. van Beneden, Sur les genres Ecteinascidia, &c., 1. c, p. 35. 



