QUADRULA 813 
Diplodon menziesii of New Zealand occasionally have some 
embryos in the outer gills. One or more examples of the 
Anodontoides ferwssacianus, which the writer examined, had 
more or less young in the inner gills. And in the Quadrulas 
all four gills are filled, though the outer are usually thicker and 
more pad-like. Now, if these are transition forms, it would 
also be reasonable to expect that the beak sculpture would 
sometimes be neither radial or strictly concentric. In most of 
the Quadrulas the beak sculpture seems to be a sort of com- 
promise between the two patterns, consisting of parallel bars 
arranged in zigzags or chevrons. In many of the species of 
this genus and of allied groups there are a few strictly radial, 
delicate ridges either before or behind the main sculpture. 
In Volume XV, page 53, of the Nautilus, Dr. H. von Ihering 
has applied the name Quadrulinae to the Quadrulas and allied 
forms. My reason for not giving them the rank of a subfamily 
is that in the character of the shells, their beak sculpture and in 
the anatomy they seem much more nearly allied to the Union- 
ine than to the Hyriane. 
Section CRENODON’TA Schliuter. 
Crenodonta SCHLUTER, Virz. meiner Conch., 1836, p. 33.—Orr- 
MANN, Ann. Car. Mus., VIII, 1912, p. 245. 
Shell more or less alate; beaks prominent; the surface of 
the valves usually sculptured with oblique folds; posterior 
slope generally. having smaller radial plications, which curve 
upward behind; epidermis brownish or blackish ; anterior mus- 
cle scars large, distinct, very shallow, the anterior edge 
smooth, the rest apparently filled with roughened shelly mat- 
ter ; posterior scars large, shallow, indistinct ; escutcheon large 
and dark. 
Animal with the gills generally large, rounded below ; inner 
the larger, usually free nearly or quite the entire length of the 
abdominal sac, the two pairs united to the mantle nearly, but 
not quite, to the posterior end, having a small portion free; 
marsupium occupying all the four branchize, forming very 
heavy, thick pads; labial palpi usually large. 
Type, Unio plicatus Say. 
