322 MANUAL OF THE MOLLXJSCA. 



Type, T. pubescens, PI. XXIII. fig. 9. 



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

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

 minent, with a crescentic ossicle ; pallial sinus shallow. Quter shell layer 

 composed of distinct, nucleated cells. 



Animal vnfta 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, are found in the crevices of rocks, 

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



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

 China, Sooloo : 4110 fms. 



Fossil, 30 sp. (Trias ?) L. Oolite . U. States, Europe. 



PHOLADOMYA, G. Sowerby. 



Recent Type, P. Candida. PL 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 furrowed, without 

 radiating ribs ; 6 sp. Oolites, Europe. 



MYACITES (Schlotheim) Bronn. 



Syn. Myopsis (Jurassi) Ag. Pleuromya, Ag. Arcomya (Helvetica) Ag. 

 Mactroinya (mactroides) Ag. Anoplomya (lutraria) Krauss. 



JSx. 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. TJ. S. Europe, S. Africa. 



Sub -genera ? Goniomya,&%. My a 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. 



Tellinomya (nasuta) Hall; Silurian, U. S. Europe. Not characterised. 



? Grammysia, Yerneuil. Nucula cingulata, His, U. 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. 



