MALACOZOA. TROPIOPODA. LAMELL1BRANCHIATA. 299 



It occurs also in the Harbour of Aberdeen. It forms a soft 

 bed, communicating with the surface by a narrow passage, by 

 which the tube is protruded, and sinks to the depth of from 

 nine to fifteen inches. 



Mya arenaria. Linn. Syst. Nat. i. 1112. — Mya arenaria. Penn. 

 Brit. Zool. iv. 79. PI. 42; Ed. n. iv. 161. PI. 45.— Mya arenaria. 

 Mont. Test Brit. 30. — Mya arenaria. Turk Brit. Biv. 32. — Mya 

 arenaria. Lamk. Syst. v. 461; Ed. n. vi. 74. — Mya arenaria. Flein. 

 Brit Aniin. 463. 



3. Mya ovdlis. Oval Gaper. 



Shell ovato-elliptical, rounded and somewhat reflexed be- 

 hind, convex, moderately thin, rugose, covered with a greyish- 

 yellow epidermis extending over the mantle-tube ; the right 

 valve with a broad, abruptly terminated, concave tooth ; the 

 left with a small depression, having anteriorly a rather thin 

 prominence, and posteriorly two oblique ridges ending in a 

 rather pointed prominence ; the umbones nearly central ; the 

 colour of the shell dull white, of the interior glossy white. 

 Length ten-twelfths of an inch, height six-twelfths. 



Brought up by fishing-lines from the Bay of Aberdeen ; 

 also sometimes found on the beach. 



As Turton observes, " it has the convexity of Mya truncata, 

 with the rounded anterior end of the Mya arenaria, but not 

 so much produced." He gives Clontarf in Dublin Bay, and 

 Torbay in Devonshire, as localities. 



Although Dr. Fleming says, " it seems nothing more than 

 the young of Mya arenaria," I think it much more resembles 

 the young of Mya truncata, which is not truncated like the 

 adult. 



Mya oralis. Turt Brit. Biv. 33. PI. 3. f. 1, 2.— Mya arenaria. 

 Young. Fleni. Brit. Anim. 463. 



Genus 2. Lyonsia. 



Shell oblong, much compressed, inequivalve, inequi- 

 lateral, open at the posterior end, concentrically striated, 

 covered with an epidermis which is prolonged upon the 

 mantle and tubes. Umbones very small. Hinge tooth- 

 less, but with an intervening calcareous body connected 

 with the ligament, which is internal, and in each valve 

 an oblique sinus under the umbo. Muscular impres- 

 sions distant, large ; inner layer pearly. 



