60 AKERA. 



the valves being limited to the narrow space to which they are 

 confined, or else the valves themselves being soldered into the 

 tube, renders it unnecessary for them to have a ligament to keep 

 them in their places. The genera Pholas, Teredina, Fistulana, 

 and Septaria, belong to this family, which corresponds in part 

 with the families Tubicolaria and Pholadaria, of Lamarck. 



ADNA. Leach. One of the genera separated by Leach from 

 Pyrgoma, and characterized as consisting of an upper valve, 

 supported on a funnel-shaped base, which is not buried in the 

 coral to which it is attached, like Pyrgoma, but is seen 

 externally. The operculum consists of four valves. Adna, fig. 32. 

 British Channel and Mediterranean. 



ADNATE. A term applied by some authors to those shells belong- 

 ing to the family of Unionidse, which have the valves joined 

 together at the dorsal margin, not like other bivalves, by a 

 distinct ligament, but by the substance of the shell itself, the 

 valves appearing to grow together in such a manner that they 

 cannot be separated without one of them being broken as will be 

 seen in our figure of Dipsas plicatus, fig. 142. This circumstance 

 has been made the foundation of specific and even generic dis- 

 tinctions, for which however it is insufficient, because many 

 species which when young are " adnafe," when fully grown 

 have their valves joined together only by a ligament ., 



iEGLIA. Say. A division of " Unionidae," described as having the 

 " shell cuneate ; bosses prominent ; cardinal teeth much com- 

 pressed, placed on one side of the bosses. iEglia ovata, Say. 

 Occidens Lea. Am. Tr. iii. pi. 10." Lardner's Encyclopedia of 

 Malacology. 



AGANIDES. Montf. Orbulites, Lam. 



AGATHIRSES. Montf. Siliquaria, Auct. 



AGINA — ? Belongs to Saxicava, Auct/ 



AKERA. Bl. The fourth family of the order Monopleurobran- 

 chiata, Bl. containing the genera Bulla, Bullsea and Bellerophon, 

 ■which, excepting the last, constitutes the family Bullseana, Lam. 



AKERA. A genus of extremely light, horny shells, resembling 

 Bulla,, from which it differs, in the outer lip being separated 



