1895. PROCEEDINGS OF THE NATIONAL MUSEUM. 317 



though slightly pearly, i8 dull, and their beaks are plicately sculptured 

 so far as I have been able to observe, while those of Mycetopus are 

 smooth. All of these Old World forms have a vestige of a lateral 

 usually in each valve, while the South American species are either abso- 

 lutely edentulous or present slight traces of taxodout teeth. These are 

 sometimes so faint and so concealed uuder the external layers of nacre 

 that they can only be seen with a strong glass and a good light, but I 

 have observed them in several specimens. Besides this the two groups 

 are separated by half the diameter of the globe, and I know of none 

 found fossil at any intermediate points. 



There is a shell described by Higgins as Mycetopus falcatus,^ which 

 he states came from tlie Upper Amazon, but which 1 am inclined to 

 believe is oriental. It has the dull color of the recognized species of 

 SoJenaia, and the anterior basal portion of the shell is drawn down into a 

 curious projecting lobe. M. falcatns might be almost taken for a dimin- 

 nutive form of Solenaia soleniformis, Lea, from South; astern Asia. 



Some of the species of Solenaia closely resemble Anodonta angidata 

 of California, and it would not surprise me if the young of the former 

 might sometimes be found with rudimentary cardinal teeth, or that this 

 so-called Anodonta, which seems to be an aberrant form with a strongly 

 developed foot, should prove to be a Solenaia. 



Sowerby credits to Australia one species of the genus under considera- 

 tion. This is tXia Mycetopus rugatus of Sowerby, described in the Cou- 

 chologia Iconica.^ It is irregularly, concentrically wrinkled, and the 

 anterior basal portion is somewhat produced, like that of Lea's 71/. 

 emarginatus, while the posterior part is wide and obliquely truncated, 

 after the manner of Lea's si)e(des, to which it is no doubt closely related. 



If these two genera are separated, Solenaia, which is oriental, being- 

 placed in the Unionida', and Mycetopus, a strictly occidental group, in 

 the IMutelidie, as I believe they must be, they do not support the theory 

 of a connecting antarctic continent, or render it necessary to account 

 for their distribution. Ihering has separated the genera as I do, but 

 places them both in the Mutelida*.^ 



The following genera have been referred to the Unionid.T, but their 

 rank and position are extremely doubtful, or they belong elsewhere, 



AustraUella, Tennison Woods,^ has concentrically sculptured valves, 

 but is not nacreous and therefore not a Naiad. 



Jolya, Bourguignat,^ has been placed near Mutela by its author, but 

 is probably a marine or brackish water form. 



Byssanodonta, d'Orbigny,"^ of the Parana Eiver, has been often put 

 in the Unionidse near Anodonta, but it belongs in the Mytilidae. 



1 Proc. Zool. Soc, London, 1869, p. 179. 



2 Volume XVI, Mycetopus, No. 7, 1868. 



3 Archiv fiir Natnrg., 1893, p. 52. 



♦Trans. Roy. Soc. Vict., XVII, 1881, 1882, p. 82. 

 * Lettres Malacologiqnes, pp. 42-44, 1877. 

 6 Voy. Aui. M^r., p. 621, 1846. 



