76 THE NAUTILUS. 



snails (but without thread-like striae such as Planorbis frivol vis has). 

 Spire narrow, deeply sunken, with steep sides; the summit of the 

 whorls acutely angular. Umbilicus deeply funnel shaped, the base 

 of the whorls so narrowly rounded as to appear almost angular. 

 Whorls nearly 5, the last very large, rounded at the periphery, some- 

 what flattened and sloping above, more convex below it. Aperture 

 but slightly oblique, irregularly ovate, angular or subangular above, 

 broadly rounded below, the peristome slightly expanded. 



Diam. 36, height 24.5 mm. 



Diam. 34, height 22 mm. 



Lower Cape Fear River in the vicinity of Wilmington, North 

 Carolina, collected by Mr. Wm. P. Seal. 



This species is remarkable not more for its size than for the great 

 width, far exceeding any other species. It differs from P. trivolvis, 

 animon and their allies in the surface sculpture and narrower umbili- 

 cus. Planorbis corpulentus Say is also somewhat related, but its 

 differential features will be obvious in a comparison with Mr. Bryant 

 Walker's illustrations and description of that species, NAUTILUS 

 XIII, p. 133, plate 3 (April, 1900). 



OBSERVATIONS ON THE BYSSUS OF UNIONIDJE. 



BY L. S. FRIERSON. 



Recently, while collecting young or very small Unionidse, two 

 species were obtained having a byssus. Seven or eight specimens of 

 Lampsilis texasensis Lea, were taken so provided, and one specimen 

 of Lampsilis faHaciosus Simpson. The L. texasensis varied from 

 one-eighth to one-half inch in length, while the />. faUaciosus was 

 five-eighths of an inch long. 



The size of the shell and the length of the byssus did not appear 

 to bear any constant ratio, nor did the size (or diameter) of the 

 byssus vary. The most of the texasensis and also the faUaciosus were 

 taken by means of a combination flour scoop and sieve such as is 

 used in our kitchens. This was used to scrape up the bottom, and 

 then the mud washed out leaving the larger stuff behind. In this 

 way the original position occupied by the shells could not be ascer- 

 tained ; but several specimens were taken attached to sticks, and 

 these were hanging suspended in the water clear of the bottom. 



