DORIS DEPRESSA. 



D'Orbigny's genus Vittiersia is founded upon a Boris of this division imperfectly understood. 

 It requires no great stretch of imagination to convert the spiculous armature of the cloak, in 

 our species, into a calcareous shield, and the branchial plumes are so very minute, that it is 

 difficult to recognise their plumose character. M. D'Orbigny describes and figures a circle 

 of what he calls mamilla (marnebn), corresponding to the plumes in our species, but does not 

 assign them any function. What he calls the branchiae were probably the ovigerous vesicles 

 of a small crustacean of the Lernea tribe, which is parasitical on the nudibranchs, and, 

 burying itself entirely under the skin, shows nothing externally but two ovate processes, that 

 have the appearance of belonging to the mollusk itself.* Under this view of the subject, the 

 anomalous characters stated to belong to the supposed genus Vittiersia entirely vanish, and 

 the animal on which it was founded falls naturally into its place among the Dorides. 



Doris depressa is generally found adhering to a species of Lepralia, incrusting the under 

 side of stones in pools, near low-water mark, and so nearly resembles the zoophyte in colour 

 as not to be detected without a close inspection. This circumstance, with the minute size 

 and extreme flatness of the animal, may account for its having been so seldom observed, 

 though the distant localities in which we have found it, — Northumberland and Devonshire, — 

 show a tolerably wide range of distribution. It must still, however, be considered a rare 

 species. It is of very sluggish habits, moving seldom and very slowly when in confinement. 

 We have taken the spawn in September: it is deposited in a slender, depressed thread, 

 arranged in a delicate, close, and regular spiral coil of nine or ten volutions ; the ova are 

 placed two or three abreast, and are of a delicate salmon-colour, not much differing from that 

 of the Lepralia, on which it and the Dorides are usually found. 



Figs. 1, 2. Doris depressa, different views. 



3. A portion of the cloak, showing the tubercles. 



4. A tentacle. 



5. A branchial plume. 



6. Spicula. 



7. Spawn. 



8. A portion of the same, showing the ova. 



* Montagu describes "two pink oval vesicles" among the branchial papilla? on the back of his 

 Doris ceerulea, which are evidently the ovaries of this little parasite ; and we have ourselves been occa- 

 sionally deceived by their occurrence on other species, before we were acquainted with their true 

 character. 



