COJTCSirEEA. 455 



Type, C. HibemicTim, PL XIX., Pig. 5. C. aliforme, 

 Pig. 254. 



Bhell, equivalve trigonal, conical and gaping infront, truncated 

 behind, with a long siphonal tube near the umbones ; anterior 



Fig. 251. Conocardium aliforme, Shy^ Carb., Ireland. (Mus. Tennant.) 



slope radiately, posterior obliquely striated ; margins strongly 

 crenulated within ; hinge with anterior and posterior laminar 

 teeth ; ligament external. 



The truncated end has usually been considered anterior, a con- 

 clusion which seems incompatible with the vertical position and 

 burrowing habits of most free and equivalve shells ; if compared 

 with Adacna (Pig. 253) the large gape (a) will be for the foot, 

 and the long tube (s) siphonal. (7. Hihernicum has an expanded 

 keel, like Hemicardium inversiim>. The shell-structure is pris- 

 matic-cellular, as first pointed out by Sowerby ; but the cells 

 are cubical, and much larger than in any of the Aviculadce. In 

 Cardium the outer layer is only corrugated or obscurely pris- 

 matic-cellular. 



Fossil f 30 species* U. Silurian — Carb. North America, 

 Europe. 



Pamily XI. — LtrcEsriD^. 



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

 or obsolete ; interior dull, obliquely furrowed ; pallial line 

 simple ; muscular impressions 2, elongated, rugose ; ligament 

 inconspicuous or sub-internal. 



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

 two siphonal orifices behind; foot elongated, cylindrical, or 

 strap-shaped {ligulate), protruded at the base of the shell ; gills 

 one (or two) on each side, large and thick, oval; mouth and 

 palpi usually minute. 



The Lucinidis 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. 



Pig. 255 represents the animal of a species of Diplodonta, 



