DIANCHORA.. 148 



oarpeov, ostreon, oyster.) Ostrea Crista-galli, and otlier species 

 which are attached to stems of sea- weed and corallines, by means 

 of arms thrown out from the inner surface of the lower valve. 

 Ostrea Folium. PI. x. f. 181. 



DENTALITJM. Linnaeus (Bens, a tooth.) Fam. Maldania, 

 Lam. Order, Cirrobranchiata, Bl. — Bescr. Tubular, arched, 

 increasing in size towards the anterior extremity, open at both 

 ends ; small aperture sometimes having a lateral fissure ; large 

 aperture round ; external surface ribbed, striated or smooth. — 

 Obs. The well known shells composing this genus are shaped 

 very much like an elephant's tusk, and are not liable to be con- 

 founded with any other genus. The fossil species are some- 

 times termed Dentalithes, from dens, a tooth, and lithos, a stone. 

 The Dentalia, being true molluscs, are not rightly placed among 

 the Annelides. D. octogonum. Eound on sandy shores in 

 most climates. PL i. f. 2. 



DENTATED. Having teeth or raised points. 



DENTICULATED. (Denticulatus, Lat.) Having little teeth 

 or raised points. 



DEPRESSED. Flattened, pressed down, as the spires of some 

 shells. 



DEXTEAL Spiral Shells. Place the point of a spiral shell towards 

 the eye, with its mouth downwards ; if, as in most instances, the 

 aperture be on the right side of the axis, it is a dextral shell, if 

 otherwise, it is sinistral or reversed. Balea (fig. 296), and 

 Clausilia (fig. 295), are examples of reversed shells. 



DEXTEAL Yalve. Take a bivalve shell closed, place it before 

 the eye, with the umbones uppermost, and the posterior side, 

 which may be known by the ligament towards the observer, 

 whose right side will then correspond with the right valve of 

 the shell. 



DIADEMA. Eanz. Coeoktjla Diadema, Auct. PI. i. fig. 17. 



DIADOEA. Gray. Cemouia, Leach. 



DIANCHOEA. Sowerby. Fam. Pectinides, Lam. Order, Pal- 

 liobranchiata, Bl. — Bescr. Inequivalve, attached, oblique, sub- 

 triangular ; attached valve, having an opening in the place of 



