ANNULUR OPERCULUM. 67 



the species with short flattened spires, have rounded, and others 

 angulated apertures. North America. An example of each is 

 represented, fig. 314. 



ANCYLUS. Geoffroy. Fam. Calyptracea, Lam. Otides, Bl. — Descr. 

 Thin, obliquely conical, patelliform ; apex acute, turned sidewise 

 and backwards ; aperture oval ; margin simple. — Obs, Although 

 the little fresh-water shells described under this name, resemble 

 those of the genus Patella, the animals which produce them are 

 nearly allied to the Lymneanse. And, it may also be observed, 

 that the shells themselves differ from Patella in not being quite 

 symmetrical, having the apex turned on one side. A. fluviatilis, 

 fig. 246. Found in Great Britain, and in Southern and Central 

 Europe, West Indies, &c. 



ANDROMEDES. Montf. Vorticialis, Lam. Fam. Nautilacea, 

 Lam. A genus of microscopic Foraminifera. 



ANGULATED. (Angulatus.) Having an angle, or corner, as the 

 anterior of the aperture of Eulima, fig. 348 ; the posterior side 

 of Castalia, fig. 140 ; the whorls of Carocolla, fig. 277. 



ANGULITES. Montf. A genus composed of species of fossil 

 Nautili, described by De Blainville as not umbilicated, with a 

 dorsal keel and angular aperture. Nautilus triangularis Buffon. 



ANGIOSTOMATA. Bl. The third family of Siphonobranchiata, 

 Bl. described as differing little from the family of Entomostomata, 

 but having long, narrow, straight apertures, and the columellar 

 lips straight or nearly so. Were it not for the admission of the 

 genus Strombus into this family, it would correspond with 

 Columellaria and Convolute of Lamarck. 



ANNELIDES. The ninth class of invertebrated animals, divided 

 into three orders, namely, A. Apodes, A. Antennes, and A. Seden- 

 taires. The last only contains families of testaceous Mollusca. 

 The animals are vermicular, some naked, others inhabiting shelly 

 tubes. See Sedentary Annelides. 



ANNULAR OPERCULUM is one which has the nucleus central, 

 or nearly so, the other layers surrounding it in flattened rings. 

 The term concentric is also applied. See Introduction. 



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