322 MANUAL OF THE MOLLUSCA. 



Tyi)e, T. pubescens, PL XXIII. fig. 9. 



Shell oblong, nearly equivalve, slightly compressed, attenuated and gaping 

 posteriorly, smooth or minutely scabrous; cartilage processes thick, not pro° 

 miuent, with a crescentic ossicle ; pallial sinus shallow. Outer shell layer 

 composed of distinct, nucleated cells. 



Animal with the mantle closed ; foot linguiform ; siphons rather long, 

 separate, with fringed orifices; gills single, thick, plaited; palpi narrow,* 

 pointed. 



T. concentrica and T. distorta, Mont, ai'e found in the crevices of rocks, 

 and burrows of Smicava ; they have been mistaken for boring-shells. 



Distr. 10 sp. Greenland, U. States, Norway, Brit. Medit. Canaries, 

 China, Sooloo: 4—110 fms. 



i^o.«7, 30sp. (Trias?) L. OoHte -. U. States, Europe. 



Pholadomta, G. Sowerby. 



Recent Type, P. Candida. PI. XXII. fig. 15. I. Tortola. 



Shell oblong, equivalve, ventricose, gaping behind ; thin and translucent, 

 ornamented with radiating ribs on the sides ; ligament external ; hinge with 

 one obscure tooth in each valve ; pallial sinus large. 



Animal with a single gill on each side, thick, finely plaited, grooved along 

 its free border, the outer lamina prolonged dorsally ; mantle with a fourth 

 (ventral) orifice. {Owen.) 



Fossil, 150 sp. Lias — , U. S. Europe, Algeria, Thibet. 



Homomya (hortulana) Ag. Shell thick, concentrically fmTowed, without 

 radiating ribs ; 6 sp. Oolites, Europe. 



Myacites (Schlotheim) Bronn. 



Spi. :Myopsis (Jurassi) Ag. Pleuromya, Ag. Arcomya (Helvetica) Ag. 

 Mactromya (mactroides) Ag. Anoploiuya (lutraria) Kj-auss. 



JjJx. M. sulcatus, Flem. (Allorisma, King, Pal. Tr. 1850, PI. XX. fig. 5.) 



Shell oblong, ventricose, gaping, thin, often concentrically furrowed; 

 umbones anterior; surface granulated; ligament external; hinge with an 

 obscure tooth or edentulous; muscular impressions faint ; pallial line deeply 

 sinuated. 



Fossil, 50 sp. L. Silurian — L. Chalk. U. S. Europe, S. Africa. 



Suh-genera ? Gonio7ni/a,kg. Mya literata, PI. XXII. fig. 16. (Lysia- 

 nassa, Miinster, not M. Edw.) Shell equivalve, thin, granulated; ligament 

 external, short, prominent. Fossil, 30 sp. U. Lias — Chalk. Europe. 



TelUnomya (nasuta) Hall; Sihman, U. S. Europe. Not characterised. 



? Grammysia, Verneuil. Nucula cingulata. His. V. Silurian, Europe. 

 Valves with a strong transverse fold extending from the umbones to the 

 middle of the ventral margin. 



? Sedgwickia (corrugata) M'Coy. = ? Leptodomus (senilis) M'Coy. 



J 



