THE NAUTILUS. 49 



extending in a row from above the centre of the cavity down 

 and forward upon the base of the cardinal teeth. Three well 

 impressed muscle scars in front, two behind, the later almost 

 confluent. Habitat, Kux Creek, Chama, Guatemala. Collected 

 by Mr. A. A. Hinkley, Feb. 6, 1917. A few dead specimens 

 were obtained on the bank of the Isaibha River (Chama) of 

 which the Kux Creek is a tributary. Type in Academy Natural 

 Sciences. Cotypes in collection of A. A. Hinkley, the author 

 and U. S. N. Museum. 



I place this species in Psoronaias Crosse and Fischer, type U. 

 psoricus, because of its evident relationship to crocodilarum, and 

 distindus, differing mainly from the latter in size and degree 

 of inflation, being much inferior in both respects to distincttis. 



ON THE RATE OF GROWTH OF POND UNIOS. 



BY L. S. FRIERSON. 



During the latter part of March 1916, the writer, for the pur- 

 pose of constructing a fish pond, excavated a barrow-pit near 

 the bank of a small creek, about ten feet wide, and at the time 

 nearly dry. The barrow-pit was perhaps one hundred feet long, 

 fifty feet wide and three feet deep. Early in April, 1916, the 

 pit became full of water, overflowing from the adjacent creek, 

 and together with two subsequent overflows, supplemented with 

 seepage from the newly constructed fish pond, the pit remained 

 more or less full of water, until May 25, 1917, when it was 

 drained by a ditch into the nearby creek. From the dried 

 bottom of this pit some thirty Unios were picked up by the 

 writer. Ten of these were Unto tetralasmus Say, and the rest 

 were T. texasensis Lea. All the specimens were of remarkably 

 uniform size and appearance. The texasensis being about one 

 and a half inches, and the tetralasmus two and a half inches 

 long. Exact dimensions of a texasensis: length 43, height 24, 

 diam. 16 mm.; of tetralasmus 75, 40, and 25 mm. 



Both of these species had attained puberty. A female texa- 

 sensis has its gills fairly full of young glochidia. A tetralasmus 

 had several (three or four) ovisacs with a few (remaining) 



