54 THE NAUTILUS. 



I am greatly indebted to Dr. H. A. Pilsbry for comparing 

 our specimen with material in the collection of the Academy of 

 Natural Sciences of Philadelphia. 



STUDIES IN NAIADES. 



BY A. E. ORTMANN. 



( Concluded from Vol. 29, page 67. ) 



EURYNIA (MICROMYA) ARKANSASENSis (Lea). (See: Lampsilis 

 ark. Simpson, 1900, p. 557). 



Three males and three sterile females from Saline River, 

 Benton, Saline Co., Ark., collected by H. E. Wheeler, July 

 13, 1911. 



Mantle-connection between anal and supraanal moderately 

 long, but shorter than either opening. Anal with distinct or 

 indistinct crenulations. Branchial with papillae. In front of 

 branchial, the inner edge of the mantle is slightly lamellar in 

 the female, with a series of about a dozen very small, rather 

 distant, and somewhat irregular papillae, accompanied by a 

 streak of black pigment. These papillae are smaller than those 

 of the branchial opening, and are most distinct anteriorly. 

 They are smaller than those of vanuxemensis, but agree very 

 nearly with those of constricta. In the male, the streak of black 

 pigment is present, but the papillae are represented by mere 

 crenulations. 



Posterior margins of palpi connected at base. Inner lamina 

 of inner gills entirely connected with abdominal sac. Mar- 

 supium of the sterile female with 20 to 25 ovisacs, its edge 

 pale brownish. 



This species also in the shell resembles E. vanuxemensis and 

 constricta, but it is more swollen and has more anterior beaks. 

 The female has the characteristic shape of these species, but 

 the enlarged and truncated posterior part is more evenly 

 rounded, and the posterior end not so much produced. At 

 least one of my females (the largest) has an indication of the 

 " constriction" seen in old specimens of the two other species. 



