50O SMITHSONIAN MISCELLANEOUS COLLECTIONS [vol. 50 



also in having the anterior end but slightly attenuated. An average 

 specimen measures 116 mm. long, 42 mm. wide at the beaks, and 

 52 mm. wide at the posterior dorsal angle, with a maximum diam- 

 eter of 28 mm. The corresponding measurements for a specimen 

 of the typical form are : 92.0, 33.0, 4*5.0, and 30.0 mm. 



Lea, in his original description, mentions the radiations, which are 

 still faintly visible on his type, collected nearly three-quarters of a 

 century ago. In the generic diagnosis of Gonidea in the Synopsis 

 of the Naiades (Proc. U. S. Nat. Mus., xxn, p. 657) we find the 

 expression "epidermis rayless" — an inadvertence which should be 

 corrected. 



In his communication, Mr. Hannibal gives the following interest- 

 ing data as to the habits of the species in his locality : It is found in 

 "sloping clay banks, between four inches and two feet below the 

 water level. They dig close to the surface a horizontal burrow, per- 

 haps three times their length or less, with a sloping ditch down the 

 slope [of the bank] , which they stay in when the water level falls in 

 summer. They are sometimes solitary, but usually there are two or 

 three very large ones and several small ones in the same burrow, 

 where they brace themselves very tightly. A twenty-five-yard-long 

 clay bank will often yield forty or fifty big fellows for dissection 

 work. One exception to this situs was found in an artificial pond 

 with brick walls, mud bottom, and inhabited by ducks. Here scat- 

 tered big fellows might be found all over the bottom, where they had 

 been washed in at the time of high water, and later were unable to 

 get out." 



It may be added that Mr. Henry Hemphill found the strongly 

 angulated form of the species imbedded to the level of the angle or 

 carina, in rapid streams, so that material carried along by the current 

 would slip easily over the flattened surface of the end of the valves 

 without disturbing the animal or eroding the shell. 



The form discovered by Mr. Hannibal presents such a contrast 

 to the angulate type of the species that in the absence of connecting 

 links it might easily be taken for a new species, and to distinguish 

 it from the typical angnlata I would propose for it the name of 

 variety haroldiana. Types of the variety are No. 110,596, U. S. 

 Nat. Mus. 



