398 MOLLUSCA. ARCADE. Arca. 
rior side, with the upper margin shorter, straight, and nearly 
closed. 
Balanus Bellonii, List, Conch, t. ccvii. — Musculiis striatus, Borl. Corn. 
277- t. xxviii. f. 15 — Area No£e var. Dow. Brit. Shells, t. clviii. f. 3. 
A. fusca, Mont. Test. Brit. Sup. 51. t. 4. f. 3. Turt. Biv. Brit. 167 — 
Southern coasts of England, and Frith of Forth, rare. 
This species nearly resembles the last, of which it is perhaps only a varie- 
ty. It differs, however, in being narrower, the beaks more lateral, a greater 
convexity, straighter margin, and finer decussations. 
402. A. tetragona. — Shell rhombic, with granular decussa- 
tions, and an oblique longitudinal rib, open at the margin. 
Lamk. Hist. vi. 37* Turt. Biv. Brit. 1G7- t. 13. f. 1. — At the Calves, 
west of Ireland, Dr Turton. 
“ Shell |ths of an inch long, and an inch broad, of an oblique square figure, 
tumid at the beaks, from which proceed a nearly central rib, to the angular 
point of the opposite margin ; hinge not quite straight, in consequence of the 
marginal slope ; colour whitish-brown, inside white, with a purple blotch at 
one end.” Turt. 
403. A. barhata. — Shell oblong, with longitudinal bearded 
ribs, decussated by minute strias ; the margin straight and near- 
ly closed. 
Brown., Wern. Mem. ii. 512. t. xxiv* f. 3. — A. reticulata, Turt. Biv. Brit. 
168. Found in Loch Strangford, by Dr Magee. 
Length half an inch, breadth one inch ; shell white ; cuticle chesnut ; ribs 
about twelve, nearW equidistant and flat ; inside striated longitudinally, 
margin finely crenulated. 
404. A. lactea — Shell oblong, decussated and bearded, an- 
gular at the anterior end, and slightly open at the margin. 
Pectunculus exiguus. List. Conch, t. cccxxxv — A. lac. Linn. Syst. i. 1141« 
— A. barbata, Penn. Brit. Zool. iv. 98. t. Iviii. f. 59. — A. lac. Mont. Test. 
Brit. 138.— A. perforans, Turt. Biv. Brit. 1G9. t. 13. f. 2, 3 — Different 
parts of the coast, but not common. 
Length half an inch, breadth three quarters ; shell white, with a brown 
pilose cuticle ; ribs numerous, fine, crossed by the wrinkles of growth ; inter- 
stices punctured ; inside white, margin plain. 
EXTINCT SPECIES. 
1. A. subacuta. Gibbose ; margin an obtuse scalene triangle, deepl}’’ plait- 
ed ; breadth greater than the length ; surface longitudinally striated.— /.Vower. 
Min. Conch, t. xliv. Upper fig. — In Chalk Marl. 
2. A.carinata — Very convex parallelopipedal, anterior side flattish, sepa- 
rated by an acute angle, truncated at nearly a right angle ; posterior side 
rounded ; surface longitudinally ribbed. — Sower. Min. Conch, t, xliv. Lower 
figure. — In Green Sand. 
3. A. Branderi — Transversely elongated, rhombic, gibbose, finely decus- 
sated ; beaks distant ; longitudinal striie strongest ; teeth numerous ; edge in- 
ternally entire — Sower. Min. Conch, t. cclxxvi — London Clay. 
4. A. appendiculata — Transversely elongated, rhombic, gibbose, decussated ; 
beaks rather distant ; two oblong appendages upon the space between the 
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