32 Mr. Alder and Mr. Hancock on new Mollusca. 



tacula, as in other genera of the same order. The greater 

 opacity of the skin generally prevents their being observed in 

 older individuals. In what degree the faculty of vision may 

 be possessed by these animals in different stages of their 

 growth, or whether the full-grown animal may in some in- 

 stances be deprived of a sense enjoyed during youth^ it may 

 be difficult to determine. From the feeble development of 

 these organs the sense is no doubt at any time very imper- 

 fect ; but the fact of their existence is interesting, as showing 

 a greater unity of structure in the whole of the Nudibranchous 

 order. 



Doris aspera. 



Body depressed, white or yellowish, semitransparent. Cloak filled 

 with spicula running in all directions, covered with large obtuse 

 tubercles, interspersed with a few smaller ones, not crowded ; firm 

 and rough to the touch. Dorsal tentacula long, slender, white or 

 yellowish. Branchiae consisting of nine small, simply pinnate, trans- 

 parent white plumes. Foot, when in motio^, extending beyond the 

 cloak behind. Length j%ths of an inch. 



Common among the rocks at Tynemouth, CuUercoats and Whitley. 



D. DEPRESSA. 



Body much depressed, transparent, of a pale sandy colour, spotted 

 with orange or reddish brown. Cloak covered with delicate pointed 

 papillae, and having strong imbedded spiculse arranged transversely 

 across the back and diagonally at each side. Dorsal tentacula pale 

 yellow. Branchiae consisting of ten or eleven very short, simple, 

 transparent white plumes, arranged in a horse-shoe form round the 

 vent. Foot broad, truncate anteriorly, of a pale grayish pink colour. 

 Veil above the mouth large, semicircular. Length -fyths of an inch. 



Under stones at low- water mark, Whitley ; very rare. 



D. REPANDA. 



Body depressed, of a waxy semitransparent white. Cloak widely 

 expanded, covered with minute, opake-white, granular tubercles, irre- 

 gular and rather distant ; a row of sulphur-yellow or opake-white 

 spots extends down each side. Dorsal tentacula ovate-oblong, 

 strongly lamellated, without sheaths. Branchiae small in proportion 

 to the size of the animal, of four or five broad, tripinnate, transpa- 

 rent white plumes. Foot narrow, showing the cloak much beyond, 

 which appears veined on the under side. Length -j^ths of an inch. 



Among the rocks near low-water mark at CuUercoats ; not uncom- 

 mon. 



D. SIMILIS. 



Body rather convex, transparent white. Cloak regularly covered 

 with numerous conical, opake-white papillae. Dorsal tentacula large, 

 swelling in the middle, yellowish white, issuing from short denticu- 

 lated sheaths. Branchiae of nine narrow transparent white plumes, 

 tripinnate, with a strong denticulated central rib. Veil above the 



