OSCANIUS. 219 



culated at their bases. The gill is attached two-thirds of its length 

 by a lax thin membrane. Anal duct at the posterior end of the 

 membrane, it is cylindrical, truncate and deeply crenulate at the tip. 

 Generative organs very large, immediately anterior to the gill, con- 

 nected by a prominent grooved ridge. Whole upper surface of the 

 mantle covered with a reticulation of pale bluish ash lines, inter- 

 spaces fawn color, becoming obsolete toward the margin and more or 

 less dotted with whitish. Also ornamented with a large oblong 

 dorsal spot of deep purple-brown, and a series of irregular shaped 

 spots surrounding it, of same color, all of which are dotted with pale- 

 blue. Head pale, mottled with purple-brown. Tentacles pale at 

 their tips andlineated transversely with darker. The inner portion 

 of the under side of the mantle and upper side of the foot deep 

 purple-brown. Locomotive disk bluish-ash, tinged anteriorly with 

 cream-yellow, and marked posteriorly with a purple-brown stripe. 

 Veil same color as foot. Gill deep purple-brown, generative organs 

 purple-black. Length six inches. (Pse.~). 



Huahine. 



Pleurobranchus grandis PSE., Amer. Journ. Conch., iv, p. 78, pi. 

 10, f. 2 (1868). 



This large and delicate species differs from others of the genus, in 

 the mantle being extended over the head and notched for the accom- 

 modation of the tentacles ; also in the attachment of the branchial 

 plume to the body and the plumules being tuberculated at their 

 base, for reason probably of the large size of the gill. After close 

 examination of several specimens no shell was found. (Pse.). 



Closely allied to the next species. 



O. BLAINVILLII Lesson. PI. 49, fig. 42. 



Length nearly 3 inches, alt. 2i- inches. Dorsal disk thin, flat, 

 fleshy and oval, rounded behind, having a sinus in front ; of the 

 bluish-white color of porcelain, with white striae and some purplish 

 rays in the middle; ochrey red toward the anterior border; buccal 

 tentacles and generative organs purple-black. Gill an elegant, bi- 

 pinnate plume of purplish color. Violet rose tints the body and is 

 grooved by ramifying bluish striae. The foot is flat, smooth, bluish- 

 white, thicker and colored with carmine at the edge ; it is rounded 

 in front and terminates in an obtuse point posteriorly. 



Point Venus, Bay of Matavai, Tahiti (Lesson). 



