OF MOLLUSCA. 175 



Lingual membrane very narrow. Teeth in arched cross series, black- 

 tipped. 



Head, tentacles, sides of feet and edge of mantle of Patella com- 

 pressa deep violet-blue ; foot violet-grey ; gill yellow. Cape of 

 Good Hope, living on the stems of Fuci (not seen on the shores). 



The Messrs. Adams have formed a subgenus, Cymbula, for Patella 

 compressa, which is only a variety of form, produced by the situation 

 where it lives, of Patella miniata, arranged by them with the true 

 Patella. Specimens with the two species combined in the same 

 individual are not very rare. The subgenus Scutellastera of the 

 same authors, I fear, is not more distinct. 



The edge of the mantle of Patella oculus is deeply lobed, sub- 

 stellate like the shell. 



The edge of the mantle of Patella testudinaria is fringed with a 

 series of minute tentacula. 



The gills of Patella Testudo are, like those of P. vulgata, united 

 over the head. 



Patella insessa, with a small horny brown shell with three or four 

 white markings on the apex, is always found imbedded in the fronds 

 of a Laminaria at California, often so deeply that it must be cut out 

 with a knife. — Hinds, Voy. Sulph. 53. 



2. Olana. 



Shell ovate, depressed, narrowed and produced in front ; apex 

 obtuse, subcentral ; aperture broad, narrowed in front. Foot ovate. 

 Head rather produced. Tentacula short. Mantle much produced 

 and attenuated in front. Gills not interrupted over the head. Mus. 

 Paris. 

 1. O. cochlear. 



** Gills interrupted over the head. 



3. Patina. 

 Gills interrupted over the head. Shell oblong, smooth, pearly 

 within ; aperture simple. 

 1. P. cserulea, t. 70. f. 4, t. 268. f. 1. 



They live imbedded in holes they form in the roots of the larger 

 Fuci or Laminaria, or on the frond ; when in the former situation, 

 they are thick, with a curved base ; when in the latter, thin and flat- 

 based. 



Central teeth of Patina pellucida on each side three, of which two 

 are nearly equal, elongated at the base, flat, jointed in the middle, 

 behind within curved and produced; the inner one more slender, 

 linear, with the tip claw -like, hooked, the outer one broadish ; outer 

 margin produced in front, tip wide, subtriangular, hooked ; the third, 

 posterior, somewhat rectangular, furnished with an oblique cutting 



