49 



NOTES ON THE STRUCTURE AND HABITS 

 OF JORUNNA JOHNSTONI. 



By WALTER GARSTANG, M.A., 

 Naturalist on the Staff of the Marine Biological Association. 



The nudibranch Jorunna Johnston i, or Doris Johns toni, as it was 

 called before the old genus Doris was subdivided, received a careful 

 description at the hands of Alder and Hancock in their well-known 

 monograph, and characteristic figures of the species are given in the 

 same place. Another figure may be found in Prof. Mcintosh's " Marine 

 Invertebrates and Fishes of St. Andrews," Plate II, fig. 16. The 

 species has a fairly general distribution around our coasts, and may 

 be readily identified from Alder and Hancock's excellent description. 

 In the present communication several points in its external form and 

 habits that merit attention will be described. 



At Plymouth, Jorunna Johnstoni can be generally obtained at 

 low water from the large loose stones which lie on the northern side 

 of the great breakwater, and also from the Renny Rocks ; but 

 although a constant inhabitant at these places, it is never found in 

 large numbers. Unlike Doris tuberculata and other allied species, it 

 is not gregarious ; and it also appears to be of stationary habit and 

 averse to migration. 



Its form is, in general, depressed, and its contour extremely 

 variable. When in motion it usually assumes a narrow and elongated 

 form, the posterior end of the foot projecting slightly from beneath 

 the dorsal fold ; but when at rest, the body usually broadens out 

 until the outline is decidedly ovate, sometimes even circular, the foot 

 being entirely concealed. The colour of J. Johnstoni is well 

 described by Alder and Hancock as "generally yellowish white or 

 pale cream-coloured, occasionally of a buffish orange or lemon 

 yellow." It is not uniform, however. The rhinophores and anal 

 tube are more or less deeply tinged with brown ; and the back 

 presents a mottled appearance, owing to numbers of darker spots 

 which are scattered all over it. These spots are mostly of a pale 

 brown or fawn-colour, and are small in size, but in addition there are 

 always present a few rather larger spots which are conspicuous from 

 their dark chocolate-brown or blackish colour and from their more or 

 less regular arrangement. They are five or six in number, and are 

 situated at various points upon three imaginary longitudinal lines, 



