6 ARCA. ARK. 



pression roughened by two or three slight longitudinal 

 ridges, and in the smaller valve forming a raised transverse 

 ridge, which is grooved along the middle, and reflecting at 

 the sides for the purpose of receiving the processes of the 

 opposite valve, with two small reflected tooth-like projec- 

 tions near the middle of the shell, and a small erect one at 

 the hase of each : length about an inch , breadth seven- 

 eighths of an inch. 



Found by Mr. Fleming in the Shetland Islands: very rare. 



10. Anomia cylindrica. Cylindrical Boat-shell. 



Anomia cymbiformis. Linn. Trans, viii. pi. 3. f. 6. 



S'.iell oblong-oval, thin, semitransparent, brownish* 

 wlii.e, strongly wrinkled or striate transversely, the wrin- 

 kles often rising into thin membranaceous scales which 

 turn downwards and are nearly incumbent on each other ; 

 the upper-valve convex, more or less cylindrical according 

 to the substances on which it is fixed, narrowed towards the 

 top, tumid and turned in at the beak over the under valve, 

 which is flat and perforated near the top ; inside glossy- 

 white : length nearly half an inch ; breadth about a third 

 of its length. 



We find this shell frequently on the Devonshire coast, 

 attached to Fuci, consequently of a less cylindrical form 

 than when it adheres to Sertularise, or the spines of the 

 Echinus, v. v. 



ARCA. ARK. 



Shell of two equal valves : hinge with numerous 

 teethj alternately locking within each other, 



A. With the margin notched. 1, to 4. 



B. With the margin very entire. 5, to 11. 



1. Area pilosa. Downy Ark. 



Lister, pi. 247- f. 82 Pennant, pi. 61. f. 1 Da Costa, 

 pi. 11. f. 2 Dorset Cat. pi. 11. f. 2-^Linn. Trans. vi ? 

 pi. 18. f. 1, 2, and viii. pi. 3. f. 4. ^ 



Area Glycymeris. Donovan, pi, 37? 



Shell thick, convex,with the sides exactly equal or rarely 

 a little flexuous on one side^ covered with a dark-brown 

 downy skin, particularly round the margin, with obscure 

 bruad rounded remote ribs, minutely striate both longitiif 



dimilly 



