174 



SYSTEMATIC ARRANGEMENT 



* Gill continued over the head. 



1. Patella. 

 Gill continued over the head of the animal. 



1. P. compressa, t. 70. f. 1. 



2. P. granulans, t. 70. f. 2. 



3. P. Scutellaria, t. 70. f. 3. 



4. P. cserulea, t. 70. f. 8. 



5. P. vulgata, t. 70. f. 10, t. 70*. f. 1, 2?, 6?, t. 110*. f. 1-8 ; Forbes 



fy Hartley, B.M. t. C.C. f. 1. 



6. P. pyramidata, t. 70*. f. 3. 



7. P. crenata, t. 110. f. 2. 



8. P. Lowei, t. 110. f. 1. 



9. P. Testudo. 



Kg. 93. 

 Teeth of Patella vulgata. 



Central teeth of Patella vulgata on each 

 side three, two of which are equal and linear, 

 the hase elongated, flat, behind produced on 

 the inside, winged on the outside, longer, tip 

 recurved, with a claw-like hook, simple, keeled, 

 black ; the third, posterior, wider, at the base 

 rounded and produced on the outside, with 

 an oblique recurved cutting edge, armed with 

 three divaricating teeth ; teeth of lateral series 

 linear, flat, with a very short hook (fig. 93) . — 

 See Osier, Phil. Trans. 1832, t. 14. 



How some Patella vulgata exist is a my- 

 stery ; they are often fixed for months, perhaps 

 years, on rocks, at altitudes where they can rarely, if at all, be aspersed 

 by the sea, and are debarred access to marine vegetables ; their re- 

 corded descents from high levels, and periodical exits from, and 

 returns to, the identical hollows they have made, after feeding on 

 algae, have almost a fabulous complexion ; zones of sand fifty yards 

 wide often intervene between them and such food, and their exceed- 

 ingly slow locomotion is opposed to such manoeuvres. — Clark, Moll. 

 261. 



The gills of Patella vulgata form a continued row within the 

 margin of the mantle, but interrupted on the right side, where the 

 blood enters the gills. The foot is divided longitudinally into two 

 equal parts, the milt and eggs occupying the right side of the foot. 

 They often move from place to place, as may be observed by the 

 trail they leave in the slight coating of mud left on the rocks by 

 the water as the tide falls. The younger animals appear to be most 

 active. When attached to soft rocks, as chalk, it forms a cavity 

 which is divided into two divisions by a cross ridge ; the hinder 

 division is the deepest, and there is no lunate ridge, as is formed by 

 the animal of the genus Hipponyx (Fool's-cap). 



The mantle of Patella with black rays, from the Sandwich Islands, 

 is simple, with a crowded series of laminse on the under side of the 

 mantle near the union with the foot, interrupted over the head. 



