MONOMYAIRA. 



107 



Genus 1. — LINGULA. — Lamarck. 



Generic Character. — Subequivalve, flat, ovate-oblong, apex 

 truncated, slightly pointed at the base, elevated on a tiesby ten- 

 dinous peduncle, attached to marine bodies ; hinge without 

 teeth. 



Lingula anatina. — The Duck Lingula. Plate XIV. fig. 

 7. Shaped like a duck's bill, with a green, shining epidermis, 

 and having a cylindrical pedicle. Four inches long. Inhabits 

 the Indian ocean. 



Genus 2.— T ERE BRAT UL A.— ZamarcJ^. 



Generic Character. — Inequivalve, regular, subtrigonal ; at- 

 tached by a short pedicle to extraneous marine bodies ; the larger 

 valve with a projecting umbo, frequently bent, and perforated at 

 its summit by a round hole ; hinge with two teeth ; two slender 

 osseous processes arising from the disk of the smaller valve. 



This genus contains two sections :— * Shell without furrows or striae. 

 ** Longitudinally furrowed. 



The distinction between this genus and that of the Anomia, is that in the 

 latter the perforation is always in the smaller valve, while in the Terebra- 

 tula it is in the larger one. 



Terehratula cranium. — Tn^ Skull Terebratula. Plate 

 XIV. fig. 1. Slightly ovate, ventricose; summit of the convex 

 valve produced and blunt ; with divergent strite, and the margin 

 crenulated. Half an inch long. Inhabits the sea at the Zet- 

 land Islands. 



Genus 3. — ORB I CUL A.— ZamarcA. 



Generic Character. — Suborbicular, inequivalve; without any 

 visible hinge ; under valve very thin, depressed, and adhering to 

 marine bodies ; upper valve subconic, vertex acute, and more or 

 less elevated. 



Orhicula Norwegica. — The Norwegian Orbicula. Plate 

 XIV. fig. 32. Upper valve in the form of a depressed cone, 

 with a produced and pointed summit. Inhabits the Norwegian 



