122 COCKERELL : ON TWO CALIFORXIAN NUDIBRAKCHS. 



Hermissenda opalescens (Cooper). 

 Aeulis opaIe^ce/t-'<, Cooper, Proc. Cal. Ac. Sci., 1862. 



Hermissetida is virtually a Fardina with simple tentacles. This 

 delicately tinted animal is common at San Pedro, Cal., and my wife 

 found one at La Jolla. At San Pedro it abounds on the mud-flats, 

 growing to a length of about 42 millim., there are two opal-blue lines 

 extending along the back, diverging at two or more points {i\ (j. on 

 the head, just behind it, and at the middle of the back) to admit a 

 bright orange streak ; otherwise close 'together, ])ractically forming one 

 blue stripe. There is a broad orange stripe on each side of the head, 

 passing backwards from the oral tentacles. Oral tentacles a beautiful 

 opalescent blue. Papillae easily deciduous, their central part from 

 dark brown to very pale brown, the latter colour more common ; their 

 ends white, with an orange subterminal ring. 



These characters are recorded, because Cooper's description does 

 not do them justice. 



My wife found a variety at San Pedro, in a kelp root washed up 

 by the sea. This form, from below the tides, is coloured much like the 

 kelp; the branchial papillae are brownish-orange, broadly tipped with 

 white, without the orange subterminal ring. When first found, the 

 animal had hardly any of the opalescent blue colour, but after a time 

 it became as blue as those from the mud-flats. 



The teeth are in a single row ; a long lanceolate middle denticle, 

 and about four pointed denticles on each side, the lowest very small. 

 All this is very similar to Facelina '-In/an-^, A. and H., but (a) the 

 median denticle extends far beyond the lateral ones, in e/eijans it 

 extends only a little beyond; (b.) the lateral denticles are only three 

 or four, in elnjans they are six. 



