152 



13. planiuecula, Sow. 



14. prastenuis, Pult. 



15. prisuiatica, Soto. 



16. rugosa, Lam. 



17. Sibbaldii, Sow. 



18. subrostrata, Lam. 



19. trapezoides, Lam. 



20. tnmcata, id. 



Figures. 



PI. 42. 



Fig. 228. 



Shell, showing the pouted 



Anatina subrostrata. 

 gaping extremity. 



Anatina (Anatinella) Sibbaldii. PI. 41. Pig. 225. Shell, with one 

 valve dropped to show the conspicuous spoon-shaped process contain- 

 ing the ligament. 



Genus 7. THRACIA, Leach. 



Animal; with the mantle closed except for the passage of a com- 

 pressed linguiform foot ; siphons rather long, separated to their 

 origins, and furnished with fimbriated orifices, lohich are often 

 inflated into a globular form. (Clark.) 



Shell ; ovate or oblong, more or less inequivalve and inequilateral, 

 sometimes depressed, sometimes gibbous, whitish, generally gra- 

 nosely scabrous, partially covered with a thin epidermis ; hinge 

 with a horizontal thickened fulcrum in each valve, internally 

 excavated, receiving the ligament ; ligamentary cavity open in 

 front, having in connection with it a detached crescent-shaped 

 ossicle ; ligament partly external. 



In Thracia the hinge-cartilage, or ligament, is partly external partly in- 

 ternal, and the structure represented in the preceding genera by a spoon- 

 shaped process takes the form of a thickened fulcrum in each valve. When 

 the valves are closed and the fulcra are in contact with the ligament be- 

 tween them, an opening appears internally on the anterior side, and in 

 connection with this opening there is a detached ossicle of a crescent 

 shape. It is seldom that the ossicle is preserved. Notwithstanding the 

 care with which Mr. Cuming has collected the finest series of Thracia 

 shells known, he has never obtained the ossicle. Being detached from 

 the shell, it is doubtless lost when the animal is extracted. The hinge of 

 the different species is, however, greatly modified, and it is by no means 

 certain that they all have an ossicle. It was by an English naturalist, 

 Dr. Leach, that the genus was founded, two of the largest and most cha- 

 racteristic species being natives of our own shores. The earlier British 



