80 AZECA. 



from which the genus Avicula receives its name. The Aviculse 

 are pearly within. From A. margaritiferse, a young specimen of 

 which is figured in the plates, fig. 164, is obtained oriental 

 pearls. This is an example of Meleagrina. A. Hirundo, fig. 

 163, belongs to the genus Avicula of Lamarck. It is, however, 

 needless to continue the separation, Avicula are from E. and 

 "W. Indies, Mexico, Coasts of the Pacific, Mediterranean, 

 British Islands, &c. Fossil species occur in the London clay, 

 &c. PL ix. fig. 163, 164. 



AXINEA. Poii, 1795. A generic name used by some authors 

 in preference to PECTUNCiXLirs of Lamarck, as claiming the 

 priority. 



AXINTJS. J. Sowerby. - Descr. Equivalve, transverse ; posterior 

 side very short, rounded, with a long ligament, placed in a 

 furrow, extending along the whole edge; anterior side produced, 

 angulated, truncated, with a flattish lunule near the beaks. The 

 late Mr. James Sowerby, who described this shell in the Mine- 

 ral Conchology, did not consider his genus as established, not 

 having seen the hinge. It is stated to have been previously 

 named Thyassira; but Cetptodon, Turton, is the first name 

 accompanied by true character. 



AXIS. The imaginary line, round which the whorls of a spiral 

 shell revolve. The extremities of the axis are pointed out in fig. 

 379, by the letters, a. a. See " Columella." 



AZECA. Leach. Grray, 1840. Fam. Colinacea, Lam. — Descr. 

 " Animal like Bulinus, with subcylindrical, rather obtuse shell, 

 covered vnth a polished periostraca (epidermis) ; aperture pear- 

 shaped, curved and pointed at the top ; the margin thick, obtuse, 

 united aU round and toothed; the axis imperforated." Grray's 

 edition of Turton's British Shells, page 189.— 06«. The Turbo 

 Tridens of Montagu, upon which this genus is founded, resembles 

 Bulinus lubricus in general form and character. Both these 

 shells differ from the true Bulini in having the peritreme entire, 

 and in being pellucid and glossy. Azeca differs from Bulinus 

 lubricus in having three teeth in the aperture, two on the inner 

 lip and one on the outer. Not seeing the necessity for creating 



