292 MANUAL OF THE MOLLUSCA. 



Fossil, 270 sp. U. Silurian . Patagonia S. India. 



C. Hillanum, Sby. (Protocardium, Beyr.) is the type of a small group in 

 which the sides are concentrically furrowed, the posterior slope radiately 

 striated ; the pallial line is slightly sinuated. Jura Chalk ; Europe; India. 



CONOCARDIUM, Bronn. 



Syn. Lychas, Stein. Pleurorhynchus, Ph. Lunulo-cardium, Miinster. 



Type, C. Hiberuicum, PI. XIX. fig. 5. C. aliforme, fig. 214. 



Shell, equivalve trigonal, conical and gaping in front, truncated behind, 

 with a long siphonal tube near the umbones ; anterior slope radiately, pos- 

 terior obliquely striated; margins strongly crenulated within; hinge with 

 anterior and posterior laminar teeth : ligament external. 



The truncated end has usually been considered anterior, a conclusion 

 which seems incompatible with the vertical position and burrowing habits of 

 most free and equivalve shells: if compared with Adacna (fig. 213) the 

 large gape (a) will be for the foot, and the long tube (s) siphonal. C. Hiber- 

 nicum has an expanded keel, like Hemicardium inversum. The shell- struc- 

 ture is prismatic-cellular, as first pointed out by Sowerby ; but the cells are 

 cubical, and much larger than in any of the Aviculada. In Cardium the 

 outer layer is only corrugated or obscurely prismatic-cellular. 



Fossil, 30 sp. U. Silurian Garb. N. America, Europe. 



FAMILY X. LUCINTD^. 



Shell orbicular, free, closed ; hinge-teeth 1 or 2, laterals 1 1 or obso- 

 lete; interior dull, obliquely furrowed; pallial line simple; muscular im- 

 pressions 2, elongated, rugose; ligament inconspicuous or sub-internal.l 



Animal with mantle-lobes open below, and having one or two siphonal 

 orifices behind ; foot elongated, cylindrical, or strap-shaped (ligulate], pro- 

 truded at the base of the shell : gills one (or two) on each side, large and 

 thick, oval ; mouth and palpi usually minute. 



The Lucinida are distributed chiefly in the tropical and temperate seas, 

 upon sandy and muddy bottoms, from the sea-shore to the greatest habitable 

 depths. The shell consists of two distinct layers. 



LUCINA, Bruguiere. 



Etym. Lucina, a name of Juno. 



Type, L. Pennsylvanica, PI. XIX. fig. 6. 



Shell orbicular, white; umbones depressed; lunule distinct; margins 

 smooth or minutely crenulated ; ligament oblique, semi-internal ; hinge-teeth 

 2.2, laterals 1 1 and 2 2, or obsolete; muscular impressions rugose, 

 anterior elongated within the pallial line, posterior oblong ; umbonal area 

 with an oblique furrow. 



Animal with the mantle freely open below ; siphonal orifices simple ; 



