458 MAIOJAL OF THE MOLLUSCA. 



DiPLODONTA, Bronn. 



Etymology, diplos, twin, odonta, teetn. 



Synonym, Spliserella, Conrad. 



Type, D. lupinus (Yenus) Brocchi. PL XIX., Fig. 3. 



Shell sub-orbicular, smooth ; ligament double, rather long, 

 Bub-marginal ; hinge-teeth 2.2, of which the anterior in the 

 left valve, and posterior in the right, are bifid ; muscular im- 

 pressions polished, anterior elongated. 



Animal with the mantle -margins nearly plain, united ; pedal 

 opening large, ventral ; foot pointed, hollow ; palpi large, free ; 

 gills two on each side, distinct, the outer oval, inner broadest 

 in front, united behind ; branchial orifice small, simple ; anal 

 larger, with a plain valve. 



Distribution^ 40 species. "West Indies, Eio, Britain, Medi- 

 terranean, Eed Sea, "West Africa, India, Corea, Australia, Cali- 

 fornia. D. diaphana (Felania, Eecluz) buiTows in sand. 



Fossil, 30 species. Eocene — . United States, Europe. 



? Scacchia, Philippi, 1844 ; Tellina elliptica, Sc. Shell minute, 

 ovate, posterior side shortest ; hinge- teeth 1 or 2, laterals obso- 

 lete ; ligament minute ; cartilage internal, in an oblong pit. 

 Animal with mantle widely open ; siphonal orifice single ; foot 

 compressed, linguiform ; palpi moderate, oblong. Distribution, 

 2 species. Mediterranean. Fossil, 1 species. Pliocene, Sicily. 



? Cyamium, Philippi, 1845. C. Antarcticum, PI. XIX., 

 Fig. 16. Shell oblong \ hinge-teeth, 2.2; ligament double; 

 cartilage in a triangular groove behind the teeth ru each valve. 

 Distribution, 3 species. Patagonia, Northern Europe. Fossil, 

 1 species. Tertiary, Europe. 



Ungulina, Daudin. 



Etymology, ungidina, like a hoof. 



Type,V. Oblonga. PI. XIX., Fig. 10. 



Shell sub-orbicular ; ligament very short ; epidermis thick, 

 wrinkled, sometimes black ; hinge-teeth 2.2 ; muscular im- 

 pressions long, rugose. 



Animal with the mantle open below, fi'inged ; siphonal orifice 

 single ; foot vermi-form, thickened at the end and perforated, 

 projecting from the base of the shell or folded up between the 

 gills , palpi pointed ; gills two on each side, unequal, the 

 external narrower, with a free dorsal border, inner widest in 

 fi-ont. 



Distribution, 4 species. Senegal, Philippines, excavating 

 winding galleries in coral. 



