THE NAIADES OF MISSOURI 351 
and indistinctly double-looped ridges; post-umbonal ridge square 
cornered from beaks to post-extreme; epidermis yellowish or light 
brown painted with rays broken into square or lunate blotches; 
female shell smaller, thicker, shorter and more inflated than male. 
INTERNAL STRUCTURES:—Cardinals rather low, ragged the 
the right one having four vertical subparallel ridges; interdentum 
broad; laterals stout, rather long and sharply inclined; beak 
cavities, moderately deep; nacre silvery white, irridescent. 
Sex Length Height Diameter Locality 
Ge Mola S270) SY eraubionl (Merame R., Meramec Highlands) 
ON OF UX t56 37mm (Marais des Cygnes, Athol) 
OR Or eke 513) 30mm (Miss. R., Hannibal) 
Cis SP oe 6 16mm dale ” LaGrange) 
MISCELLANEOUS REMARKS:—P. securis being more of a 
marine type of shell than fresh water renders it worthy of the 
creation of a genus. The young shell is like that of an ‘‘exquisite 
shell from the sea-shore,” so narrowly flattened is it post-dorsal 
portion of shell, so delicately painted with broken lunate rays 
and so arched forward are its compressed and pointed umbones. 
This species is not found at all in the interior north of the Missouri 
River; neither is it found in Southwest Missouri. It is rather 
common in the Osage, Gasconade and Meramec though not very 
typical as a rule. The most perfect securis is the Mississippi. 
The writer found this species from the Mississippi bearing ripe 
glochidia June 22nd; Wilson and Clark (1914, p. 52) found the 
Cumberland securts in the same gravidity June 3-16. Dr. Ortmann 
finding it gravid in late fall again fixes its breeding season as 
normally bradytictic. 
HM be od 
Genus Lasmonos Rafinesque. 
1820—Lasmonos Rafinesque, Monograph, Ann. Gen. Sci. Phys. Brux. 
1911b—Paraptera Ortmann, Mem. Car, Mus., IV pp. 331, 334, 338. 
(Type, Lasmonos fragilis Rafinesque.) 
ANIMAL CHARACTERS:—Siphonal openings large inclined to 
be tubular; supra-anal high, well separated from anal; inner 
laminae of inner gills entirely connected to visceral mass; palpi 
free their whole length post-dorsad, color of soft parts grayish with 
yellowish papillae on blackened mantle edge or branchial opening; 
marsupium kidney-shaped, consisting of several ovisacs occupying 
posterior part of outer gills; conglutinates white, leaf-like, not 
