280 ANNALS OF THE CARNEGIE MUSEUM. 
connection between anal and supra-anal moderately long. No tendency 
to unite the inner lamina of inner gills with abdominal sac.. . Anodontoides. 
a3. Beak-sculpture concentric, heavy. Mantle-connection between anal and supra- 
anal moderate. Certain forms with tendency to connect the inner 
lamina of inner gills with abdominal sac. 
bi. Hinge-teeth more or less developed, at least the pseudocardinals present. 
Marsupium with simple ovisacs. Shell subrhomboidal.. .Alasmidonta. 
bo. Hinge-teeth rudimentary. Marsupium of gravid female unknown. Shell 
Elongated. wii. Sucve oa ler che el eeomeupe ae Peabo bos ies alcay us naces eee eee Lastena. 
bs. Hinge-teeth rudimentary. Marsupium with ovisacs subdivided into trans- 
verse compartments. Shell subovate...................-. Strophitus. 
The most primitive types are undoubtedly Symphynota and Alas- 
midonta, and among them species with fully developed hinge-teeth 
are found. The most extreme modification of the soft parts is seen 
in Strophitus, while the most extreme specialization in the shell is 
represented by Anodonta (most successful adaptation to the life in 
quiet water with muddy bottom). Arcidens is peculiar in its shell 
sculpture. Anodontoides is a connecting form between a and 4s, 
but with the whole shell-structure more inclining toward aq. Lastena 
is yet rather doubtful in its position. 
It must be pointed out that comparatively few forms have been in- 
vestigated, and that further knowledge will possibly furnish the means 
for a better understanding ot the phylogeny of this subfamily. There 
surely should be Anodontine in Asia (aside from Anodonta proper), 
which possibly might be more primitive than any of those investigated 
hitherto. For the present, the most ancient types are known from 
North America, but I do not think that the subfamily originated in 
this continent. The shape of the glochidia indicates, that it started 
probably from a form near the European genus Unio, and this makes it 
more likely that the ancestral form lived in the Old World. 
Genus SYMPHYNOTA Lea. (1829.) 
(Simpson, 1900), p. 662.) 
Shell ovate or elliptic, compressed, with smooth disk, but sometimes 
with ribs upon the posterior slope. Beak-sculpture distinct, consisting 
of a few concentric bars, followed by others, which are distinctly 
sinuated,”®> or double-looped. Hinge with teeth, the pseudocardinals 
always present, the laterals present, imperfect, or absent. 
Soft parts of typical structure: outer gills alone marsupial, when 
25 See description of beak sculpture of S. costata. 
