THE NAUTILUS. 13 



THE SYSTEMATIC POSITION OF TWO SPECIES OF MUSSELS FBOX THE 



OZARKS. 



BT DR. A. E. ORTMANN. 



EURYNIA (MlCROMYA) VENUSTA (Lea). 



Lampsilis venusta Simpson, Synopsis, 1900, p. 543. Descr. 

 CataL, 1914, p. 89. 



A large number of specimens has been received from L. S. 

 Frierson, collected by A. A. Hinkley on July 30, 1914, in 

 James River, at Galena, Stone Co., Mo. 



Specimens of this lot have been sent to B. Walker, who also 

 believes them to belong to U. venustus Lea, a species closely 

 allied, on the one hand, to L. ellipsiformis (Conr.) (Simpson, 

 1914, p. 128), and, on the other hand, to L. pleasi (Marsh) 

 (Simpson, p. 129). In fact, the latter is hardly anything else 

 but a smaller and thinner venusta. I have no doubt that all 

 three group together, and very likely the anatomy will be the 

 same. Utterback (Amer. Midi. Natural, 4, 1916, p. 141) places 

 ellipsiformis in the genus Nephronaias, but I do not think that 

 this is correct, since he describes the papilla: on the mantle 

 edge. 



Call (Tr. Acad. St. Louis, 7, 1895, p. 57) believes that pleasi 

 is identical with venustus, and, according to Frierson (in 

 litt.), v&nustus is the same as ellipsiformis. Meek & Clark 

 (Bur. Fisher, Doc. no. 759, 1912, p. 19) mention, from Big 

 Buffalo Fork, Lampsilis venusta, which, according to their 

 remarks, is this form. 



Anatomy: Soft parts (366 and 3 sterile 9 9 are at hand) 

 of the usual E'wn/mo-structure. Anal and supraanal openings 

 separated by a moderate mantle connection. Anal with dis- 

 tinct crenulations, branchial with papillae. Posterior margins 

 of palpi connected at base only. Inner lamina of inner gill 

 entirely connected with abdominal sac. 



Marsu-pium in posterior half of outer gill, with a rather 

 larger non-marsupial section at posterior end. Ovisacs about 

 15 to 20. Mantle margin, in front of branchial, slightly 

 lamellar, with small, irregular papillae, which are not crowded. 



