434 THE OPISTHOBRANCHIATE 



reduction in numbers was due to migration into deeper water or to 

 death (the weather just pi-eviously to my visit had been extremely 

 cold) it was impossible to determine. One of the specimens secured 

 on this occasion had probably been attacked a day or two previously 

 by some fish, for its cerata were all extraordinarily small. They 

 had plainly been knocked or bitten off,^ and were in course of 

 recrescence, for next day they were larger in size. These observa- 

 tions support the views proposed in my former Report (1. c, pp. 

 175 and 191) as to the significance of the structui'e, colouration, 

 erectile power, and fragility of the dorsal cerata in Solids, If the 

 head of this species be touched with a blunt needle, it is at once 

 withdrawn (almost telescoped into the body), and the cerata rise up 

 from their recumbent position and become very prominent, like the 

 quills of a porcupine. This reaction is instantaneous if the stimulus 

 be strong enough. 



The size of fifteen specimens taken on October 24th, 1889, varied 

 from 5 inch to a little over 1 inch in length, only two specimens 

 being under | inch. The smallest specimen, j inch long, had seven 

 or eight rows of papillae, while the anterior angles of its foot were 

 rounded, not produced into recurved processes. In a specimen ^ inch 

 long the number of rows of cerata was fifteen or sixteen. The white 

 '' ruff " round the neck, as Mr. Cocks stated, is a good and perma- 

 nent specific character. It appears to be caused by the cerata of 

 the first two rows having each a very short hepatic diverticulum, 

 instead of one reaching to the tip of the papilla. 



The colour of the dorsal papilla3 vai-ies from a pale greenish fawn- 

 colour to a dark brown. The tips are yellowish, sometimes almost 

 white. The basal portions of the cerata of the ruff are always 

 coloured like those behind, the colour being in all cases due to the 

 hepatic caeca. 



23. -^OLTDIELLA GLAUCA, Aid. and Hanc. 



I found a single specimen of this species, nearly an inch in 

 length, under a stone at low water on the shore beneath Lord Mount 

 Edsrcumbe's winter villa on October 11th, 1890. The animal was 

 white in colour, the hepatic caeca being of a fawn-colour, deeper 

 below than above. Much opaque white was scattered on the back 

 of the head and body, on the oral tentacles, and on the cerata. 

 The curious vermicular character of the cerata, the suddenly at- 

 tenuated extremity of the broad foot, and other points, readily dis- 



* The same was the case with a number of the posterior cerata in one of the individuals 

 taken on October 24tb. 



