NODULARIA 995 
Generally solider'and more inflated than scobinata, and lack- 
ing the median depression seen in the shell of that species. 
The nacre is less brilliant and the muscle scars more impress- 
ed; the pseudocardinals are usually stronger. Yet there are 
intermediate specimens. which nearly connect the two. 
NopULARIA NUCLEUS (Lea). 
Shell very small, solid, inflated, subquadrate or subrhomboid, 
inequilateral; beaks full and high, with strong, zigzag-radial 
sculpture, which extends over the shell; dorsal outline curved ; 
anterior end slightly narrowed, rounded; base line lightly 
curved, rather full behind the middle; posterior ridge high, 
subangular, ending near the base of the shell; posterior end 
obliquely rounded, almost truncate below; epidermis pale 
green, the ridges rich green; pseudocardinals much divided; 
laterals curved, strong; anterior scars deep; posterior scars 
shallow ; nacre very brilliant, silvery, iridescent behind. 
Length 15, height 9, diam. 8 mm. 
Siam. 
Umornucleus na, Pr: Ac.. N. Sci; Phila., VIII, 1856; p:. 04; 
Ops. Vv isiss ap: 20, pls xxvii, ie 21 ; Jl. Ac. N. Sci: Phila., 
PLE 1S58;po 302, pl. xxvinw fig at: 
Margaron (Unio) nucleus Lea, Syn., 1870, p. 30. 
Nodularia nucleus Stmpson, Syn., 1900, p. 815.—HAas, Con. 
Cab mio. TOTO, ps 113, ply x; fig. 13. 
If the only shell I have seen, the type, is adult, this is the 
smallest naiad I know of. The type is solid and much inflated, 
and has the appearance of being mature. It is shorter, more 
inflated, solider and more quadrate than crispata and has much 
brighter nacre. 
NopULARIA PHASELUS (Lea). 
Shell small, elongated, subsolid, inflated, inequilateral ; beaks 
rather full and high, their sculpture apparently zigzag-radial ; 
anterior end rounded and slightly narrowed; base line nearly 
straight, full near the hinder end; posterior ridge full, rounded, 
end in a blunt point on the median line; surface nearly smooth, 
slightly corrugated on the umbonal region and dorsal slope; 
