96 ONCIDIID^E. 



but irregularly studded with wart-like tubercles of different 

 sizes, some of which have jagged edges ; the underside is 

 closely and minutely tuberculous : mantle rather thin, lining 

 the underside, and lying close above the foot ; it is greyish- 

 white, and covered with minute white specks : head broad, 

 flanked by two large semicircular lobes or lips, which are on 

 a level with the sole of the foot : mouth forming a narrow slit 

 in the middle of the unclerpart of the head, and placed length- 

 wise : tentacles very short and conical, with bulbous tips ; they 

 are contractile, as in the Limnceidce : eyes bluish-black, nearly 

 on the tips of the tentacles : foot rather narrow, squarish in 

 front, and bluntly pointed behind ; its action is the same as 

 that of a land-slug, viz. by a series of wave-like movements : 

 respiratory orifice circular, at the hinder extremity of the 

 body, between the mantle and the foot : vent tubular, placed 

 below the respiratory orifice. L. - 5. B. 0*375. 



Habitat : Crevices of the rocks, a little above high- 

 water mark, apparently feeding on Lichina pygm&a, in 

 Lantivet Bay, Cornwall (Couch and Laughrin) ; Whit- 

 sand Bay, near Plymouth (Spence Bate). In the 

 former locality it is associated with Lasa?a rubra, Rissoa 

 cingillus var. rupestris, Melampus bidentatus, and Otina 

 otis. Mr. Laughrin informs me that the Oncidium 

 comes out in warm weather and crawls about on the 

 rocks, but that it is seldom seen in the winter; and he 

 adds that they sometimes congregate in groups consist- 

 ing of as many as twenty individuals. I observed that 

 the Oncidium, on being touched or disturbed, rolls up 

 like a Chiton by bringing both extremities together. 

 When crawling, the hinder extremity is occasionally 

 notched or hollowed out. They cannot bear long im- 

 mersion in water. Audouin and Milne-Edwards (Rech. 

 pour servir a THist. Nat. du Litt. de la France) noticed 

 0. Celticum as abundant at Port de Solidor, near St. 

 Servan. 



Philippi was inclined to consider this identical with a 

 species which he described and figured as 0. nanum, from 



