NAIADES OF MISSOURI 1i5 
before maturity (‘“‘aborted’’) if disturbed. According to recent 
studies of Dr. Ortmann and Mr. Frierson Amblema Rafinesque 
should supplant all previous names for this genus because Amb. 
costata Raf. is without doubt Unio undulatus Barnes; hence the 
following nomenclature: 
(1)—Amblema plicata (Say) 1817=U. plicatus Say. =U. hip- 
popea Lea=Quadrula plicata hippopaea Simpson. 
(2)—Amblema_ plicata costata (Raf) 1820=U. undulatus 
Barnes 1823 =Quadrula undulata Simpson. 
(3)—Amblema peruviana (Iamarck) 1819 =Quadrula plicata 
Simpson. 
Note that because of the Law of Priority the local form 
(plicata Say) from Lake Erie must be considered unfortunately 
as the main species, although other than taxonomic reasons would 
not justify the recognition. 
-Amblema peruviana (Iamarck) 
(“Three Ridge,’ ‘Big Blue Point’’). 
PPOXV E=3Figs 394d B. 
1819— Unio peruviana Lamarck, An. Sans. Vert., VI, p. 71., Deshayes, 
An.:Sans. Vert., 2d ed., VI, 1835, p. ‘533; 3d. ed., Il, 1839, p. 667. 
1900b—Quadrula plicata (Say) Simpson, Pr. U. S. Nat. Mus., XII, 
Pp. 767. 
ANIMAL CHARACTERS:—Since this species is simply an Amb. 
rariplicata (Des.) with very full, high beaks and with identical 
soft parts, except a small difference of form due to a more elongated 
shell with deeper umbonal cavities, we would refer our readers 
to the description of these characters for rariplicata. Gravid 
marsupia have the same structure. Glochidia of peruviana 
are found to be semicircular, spineless, medium size, about as 
long as high (0.200 x 0.210 mm.) 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell elongate-quadrate with ven- 
tral edge rather straight, post-dorsal portion bowed, heavy and 
greatly inflated anteriorly, rather compressed posteriorly; beaks 
high, full, incurved, well placed forward, sculpture consisting of 
concentric lines forming two loops at base of post-umbonal ridge; 
undulations four to five, coarse, oblique from ventral margin to 
umbonal region across post-umbonal ridge; costae on slopes 
