52 NAIADES OF MISSOURI 
here are suggested for general use. Reference to the four sections 
of the shell or mantle edges, limited by the anterior, posterior, 
dorsal and ventral extremities, can be expressed adjectively and 
adverbially by the respective terms, ‘‘antero-ventral,”’ ‘‘ antero- 
ventrad,” ‘‘ post-dorsad,” etc. (See Plates I—III). ‘“‘Spadiform” 
(shape of a spade head) and ‘‘celtzform”’ (shape of a celt, or axe- 
head) are used as adjectives in describing glochidia. In a few shell 
measurements adoption has been made of Scammon’s term, 
‘“umboidal ratio,’ (um ra.) which is secured by dropping a line 
perpendicularly from the tips of. the beaks to the longitudinal 
axis and expressing the distance from the intersection of the two 
lines to the anterior margin of the shell as a decimal fraction 
of the entire length of the longitudinal axis. The term, “‘zuter- 
dentum,’’ is used here for the bridge between the lateral and cardi- 
nal teeth. ‘he terms, “ bradytictic’’ and “‘tachytictic,”’ as suggested 
by Ortmann, are adopted as meaning respectively, ‘long period” 
and ‘‘short period’’ breeders. The term ‘“‘diaphragm,”’ is also 
used here for the partition between the branchial and anal open- 
ings formed by the gills. 
All shell measurements are reckoned in terms of millimeters 
(mm.) and length, height and diameter are considered consecutively. 
‘‘Diameter’’ is the distance between the greatest convexities vof 
closed valves. All other usages employed in this work have been 
in such common adoption as to need no explanation. 
To make plain those parts of this catalogue,—-especially 
the Synonomy and Bibliography,—the equalities for the abbrevia- 
tions are given as follows :— 
Am. J. Conch.—American Journal of Conchology. 
Am. Jl. Sci. and Arts—American Journal of Science and Arts. 
Am. Nat.—American Naturalist. 
An. Car. Mus.—Annals of the Carnegie Museum. 
Biol. Bull.—Biological Bulletin. 
Bull. Wash. Coll—Bulletin of Washburn College. 
Bull. U. S. Mus.—Bulletin of the United States Museum. 
Bull. U. S. B. F.—Bulletin of the Unites Stated Bureau of Fisheries. 
Jl. (or Jour.) Ac .N. Sci. Phila.—Journal of the Academy of Natural 
Science of Philadelphia. | 
J. Cinn. N. Hist. Soc.—Journal of the Cincinnati Historical Society. 
Jl. Phila. A. Sci.—Journal of the Philosophical Academy of Science. 
Mal. Soc. Lon.—Malacological Society of London. 
Moll. Chicago, Pt. I—Mollusks of Chicago, Part I. 
Monog. Biv. Ohio.— Monograph of the Bivalves of Ohio. 
