NUDIBRANCHS OF THE VANCOUVER REGION 201 



of a body of the same colour as in the individual obtained, which was not 

 in any way injured. 



Genus Hermissenda (Bergh). 



Hermissenda Bergh, Beitr. zur. Kennt. der Aeolidiaden VI . Verh. d. k. k. 



zool. bot. Ges. Wien, XXVIII, 1878, p. 573. Bergh, Proc. Ac. Nat. 



Sci., Philadelphia, Pt. I, 1879, p. 81. 

 Body slender and elongated rhinophores perfoliated, tentacles 

 elongated. The dorsal papillae are arranged in oblique transverse series 

 and lie in close-set group. 



Hermissenda opalescens (Cooper). 



Aeolis (Flabellina) opalescens Cooper, Proc. Cal. Acad., ii, 1862, p. 205; 



iii, 1863, p. 60. 

 Hermissenda opalescens Bergh, Vergh d. K. K. zool. bot ges. in Wien, 

 XXVIII, 1878, p. 573; Proc. Ac. Nat. Sci., Philadelphia, Pt. I, 1879, 

 p. 82. Cockerell and Eliot, Jour. Malac, XII, 1905, p. 50. 

 Body. — The body is elongated, slender, limaciform, not sharply 

 marked off from the foot and without a distinct mantle. The dorsum is 

 smooth and bears along the side a large number of cerata lying in oblique 

 transverse series in close-set groups, the largest being on the inside and 

 the smallest outside. The first group, containing the largest cerata and 

 commencing lateral to the rhinophores, is always distinct from the rest 

 and slightly raised. In young specimens or specimens that have lost a 

 number of cerata a second and third group can also be distinguished 

 but in older and more perfect specimens they appear to form one con- 

 tinuous group. The end of the foot extends beyond the region of the 

 cerata. The cerata themselves are elongated and sub-cylindrical with 

 a blunt point in living specimens but after preservation they are usually 

 curved as Bergh (2, p. 83) states. 



Colour. — The colour of the body and cerata is subject to considerable 

 variation. Generally the colour is of a pale translucent grey or even 

 bluish grey. Along the mid dorsal region runs a narrow opaque white 

 iridescent line which passes forward from the tip of the tail to the first 

 group of cerata. Here it bifurcates and the two branches diverge narrow- 

 ing down again to pass around the inner base of the rhinophore and then 

 turning more sharply laterally to run right up the dorsal side of the oral 

 tentacles. Another line of similar colour commences on the ventro- 

 lateral margin of the foot in front of the rhinophores and passes back 

 parallel with the edge right to the tip where it also runs into the end of 

 the mid-dorsal line. In addition to these continuous lines there is also 



