CONCHIFERA. 465 
trically furrowed ; lunule impressed; ligament external; epi- 
dermis dark; hinge-teeth 2.2, the anterior tooth of the right 
valve large and thick ; anterior pedal scar distinct ; pallial line 
simple. 
Animal with mantle open; margins plain or slightly fringed ; 
siphonal orifices simple; foot moderate, tongue-shaped; lips 
large, palpi lanceolate; gills nearly equal, united behind, and 
attached to the siphonal band. 
The animal of Astarte borealis is shown in Fig. 258; mantle- 
margins free, plain, slightly cirrated in the branchial region ; 
united posteriorly by the branchial septum, forming a single 
excurrent orifice ; pedal muscles (p p), distinct from adductors ; 
pills flat, finely striated, destitute of internal partitions; outer 
Fig. 258. -Astarte boreals, var. semi-sulcata, Leach, 3. Wellington Channel. 
gill narrow, elliptical, with a simple margin ; inner gill grooved, 
conducting to the mouth. 
Distribution, 20 species. Behring’s Straits, Wellington Chan- 
nel, Kara Sea, Ochotsk, United States, Norway, Britain, 
Canaries, Algean (30—112 fathoms). 
Fossil, 285 species. Carb. —. North and South America 
Europe, Thibet. 
? Digitaria, Wood; Tellina digitaria, Lower Mediterranean, 
Fossil, Pliocene, Britain. 
Gounpra, C. B. Adams. | 
Shell minute, triangular, furrowed hinge like Astarte, with 
lateral teeth ; pallial line simple. 
Distribution, 7 species. Panama, West Indies. 
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