258 MANUAL or THE MOLLUSCA. 



Sub-genera, Neithea, Drouet. P. quinqne-costatus and other fossil sp. 

 with concavo-convex valves and distinct hinge-teeth ; the inner layers of 

 these shells are wanting in all specimens from the English chalk. 



Pallium, Schum. P. plica, PI. XVI. fig. 8. Hinge obscurely toothed. 



Hinniles (Cortesii) Defr. P. pusio, PI. XVI. fig. 10. Shell legular and 

 hyssiferous when young ; afterwards cementing its lower valve and becoming 

 more or less irregular. Bistr. 2 sp. Fossil, Trias ? Miocene — , Europe. 



Hemipecten, A. Adams. H. Porbesianns, PI. XVI. fig. 9. Shell 

 hyaline, posterior ears obsolete, anterior prominent ; right valve flat, byssal 

 sinus deep ; structure permeated by microscopic tubuli, as in Lima. 



Disir. 120 sp. World-wide; Nova-Zembla — C. Horn; — 200 ftns. 



Fossil, 450 sp. (including Aviculo-pecten). Carb. — . World-wide. 

 Lima, Bruguiere. 



Fl^m. Lima, a file. Ex. L. squamosa, PI. XVI. fig. 11. (Ostrea lima, L.) 



Syn. Plagiostoma (Llhwyd) Sby. P. cardiiforme, PI. XVI. fig. 12. 



Shell equivalve, compressed, obliquely oval; anterior side straight, 

 gaping, posterior rounded, usually close ; umbones apart, eared ; valves 

 smootb, punctate-striate, or radiately ribbed and imbricated ; hinge area 

 triangular, cartilage pit central ; adductor impression lateral, large, double ; 

 pedal scars 2, small. 



Animal, mantle-magins separate, inner pendent, fringed with long ten- 

 tacular filaments, oceUi inconspicuous ; foot finger-like, grooved ; lips with 

 tentacular filaments, palpi small, striated inside ; gills equal on each side, 

 distinct. 



The shell is always white ; its outer layer consists of coarsely-plicated 

 membranous lamellse ; the inner layer is perforated by minute tubuli, form- 

 ing a complete network. {Carpenter.) 



The Limas are either free or spin a byssus ; some make an artificial 

 burrow when adult, by spinning together sand or coral-fragments and shells, 

 Init the habit is not constant. {Forbes.) The burrows of L. hians are 

 several times longer than the shell, and closed at each end. {Charlesworth.) 

 " This species is pale or deep crimson, with an orange mantle; when taken 

 out of its nest it is one of the most beautiful marine animals to look upon, it 

 swims with great vigour, like the scallop, by opening and closing its valves, 

 so that it is impelled onwards or upwards in a succession of jumps. The 

 filaments of the fringe are easily broken off, and seem to live many hours 

 after they are detached, twisting themselves like worms." {Landsbor&ugh.) 

 L. spinosa has conspicuous ocelli, and short filaments. 



Sub-genera, Limatnla, S. Wood. L. sub-am'iculata, PI. XVI. fig. 13. 



Valves equilateral ; 8 sp. Greenland — Brit, Fossil, Miocene — . Europe. 



LimcBa, Bronu. L. strigilata, PI, XVI. fig. 14.* Hinge minutely 



* After Bronn; the figure in Brocchi does not show the teeth. 



