Terebkatula. MOLLUSCA. ACEPHALA. 3G9 



Length nearly an inch and a quarter ; breadth one inch, convex, of a black- 

 ish horn-colour ; sides abruptly turned in, and Hattened, and marked with a 

 few irregular striie ; front margin a little indented on each side, and project- 

 ing in the middle ; perforation somewhat triangular. 



368. T. aurita. — Regularly ribbed ; the large valve broadest 

 in the middle, semicircular in front, and becoming narrow at the 

 apex. 



Flem. Phil. Zool. ii. 498. t. iv. f. 5 — T. costata, Lowe, Zool. Journ. ii. 

 105. t. V. f. 8, 9.— West coast of Scotland. 

 Length about /gths, breadth ^-yths of an inch ; whitish ; the ribs, from the 

 beak to the margin, the most distinct, rounded, and about eight in number, 

 obsoletely wrinkled concentrically ; the ribs, towards the sides, indistinct ; 

 margin crenulated by the ribs ; the small valve nearly orbicular ; the hinge 

 margin subtruncated, or rather obtusely angular, and having the sides de- 

 pressed ; inner surface punctated ; jjeduncle short, of numerous unequal and 

 tubular threads attached to a complicated tendino-muscular apparatus, and 

 chiefly to the lower valve. I obtained a small specimen of this species at 

 Ullapool, in Loch Broom. The one, of a larger size, described by ]\Ir Lowe, 

 was found by Mr J. Berkely, at Oban. 



EXTINCT SPECIES. 



* Margin of the valves entire, ai- slightlg tvaved. 



1. T. suhrotunda Circular, depressed, smooth ; valves regularly and equal- 

 ly convex. — Sower- Min. Conch, t. xv. f. 1, 2. — In Chalk. 



2. T. ovata — Ovate or oblong-ovate, depressed, smooth ; small valve flat- 

 tish, slightly pentangular — Sower. Min. Conch, t. xv. £ 3. — In Green Sand. 



3. T. punctata.— ~Oh\ong, depressed ; valves equally convex ; edge straight- 

 ened at the front ; the whole surface finely punctated — Sower. Min. Conch, 

 t. XV. f. 4 — In Lias, 



4. T. carnea. — Depressed, smooth, obtusely five-sided ; front edge short ; 

 valves equally convex, slightly flattened along the middle. — Sower. Min. 

 Conch, t. XV. f. 5, 6 — In Chalk, 



5. T. sMSwniate.— Nearly circular, depressed, smooth ; valves equally gib- 

 bous ; front margin straight or slightly depressed in the middle, with one un- 

 dulation on each side of it — Sower. Min. Conch, t. xv. f, 7 — In Chalk. 



6. T. intermedia Obscurely five-sided, rather depressed, smooth ; larger 



valve most convex ; front margin undulated ; three depressions in the smaller 

 valve, and two in the larger — Sower. Min. Conch, t. xv. f. 8.— Green Sand. 



7. T. semiglobosa Nearly circular, gibbous, smooth ; largest valve deepest, 



and uniformly gibbous; front margin undulated, with two risings in the 

 smaller valve Sower. Min. Conch, t. xv. f. 9 — In Chalk. 



8. T. biplicata. — Oblong, gibbous; beak prominent; sides rounded; front 

 straiglitish when full grown, elevated with two distant large plaits.— S'omw. 

 Min. Conch. I. xc. and t. ccccxxxvii. f. 2, 3.— In Greeri Sand. 



9. T. digona. — Triangular, oblong, gibbous ; beak prominent ; sides round- 

 ed ; front either convex or concave ; when old, bounded by two promuient 

 angles, alike in each valve. — Soiver. Min. Conch, t. xcvi. — Oolite. 



10. T. oi'oi(fes.— Ovate, elongated ; beak prominent; larger valve gibbous, 

 VOL. I. A a 



