176 lEIDINA. 



within the closed part of the hinge, so as not to be seen when 

 the valves are shut. But the substance, formerly called the 

 internal ligament, is now distinguished from the true ligament 

 both in structure and use ; and is now more properly called the 

 cartilage, so that when the ligament is said to be internal, it 

 must be understood that the internal cartilage is unaccompanied 

 by any ligament properly so called, and when a shell is described 

 as having two ligaments, as in the case of Amphidesma, it means 

 that the two substances are so far removed from each other in 

 the hinge that they are no longer confounded together. 



INTEEISTAL SHELL is one which is enclosed in the soft parts 

 of the animal, as a bone is enclosed in the flesh of a human body. 

 The Limax, or common garden slug, which has a testaceous 

 shield beneath its mantle, is an instance of this. 



10. Lea, 1842. A genus composed of several species of fresh- 

 water shells which are considered as differing from Melanise in 

 having the anterior termination of the aperture produced into a 

 poiut in some degree resembling the caudal canals of shells be- 

 longing to the family of Canalifera, which are marine. lo fusi- 

 formis and spinosus are described and figured in Lea's work. 



JODAMIA. Defr. A genus resembling Birostrites, except that 

 in Jodamia one valve overwraps the other, while in Birostrites 

 the circumference of the valves is equal. 



JOTJAIS'NITIA, Desmoulins. Pholas semicandata. 



IPHIGENIA. Schum, 1817. Capsa, Lamarck. 



IPHIGENIA. Gray, 1821. A sub-genus of ClausHia, C. bipH- 

 cata, &c. Auct. Gray's Turton, p. 214. 



lEIDEA. Sw. A genus of " Hyrianse," Sw. thus described: — 

 " Oblong ovate ; bosses small, depressed, suleated ; inner car- 

 dinal tooth placed between the outer. I. granosa. Lam. En. 

 Meth. 248. fig. 9." 



lEIDINA. Lamarck, 1818. A genus belonging to the Nayades, 

 and resembUng the Akodgntje, Auct, but its peculiar charac- 

 teristic is that the hinge lamina is tuberculated or crenulated in 

 its whole length. Sowerby unites all the genera of the family 

 into the genus Unio. I. Elongata. PI. viii. fig. 150. 



