12 NAIADES OF MISSOURI 



duced here are suggested for general use. Reference to the four sec- 

 tions 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 " celtijorm" (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, " inter - 

 dentmn," is used here for the bridge between the lateral and cardi- 

 nal teeth. The 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 of 

 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. 

 Mai. Soc. Lon. — Malacological Society of London. 

 Moll. Chicago, Pt. I. — Mollusks of Chicago, Part I. 

 Monog. Biv, Ohio, — Monograph of the Bivalves of Ohio. 



