TIJK NAUTILUS. 89 



The identifications have been made for the greater part by H. A. 

 Pilsbry and W. H. Dall, and for this and other courtesies thanks are 

 hereby extended. 

 Margaritana mar garitifera L. 



This is the only species of bivalve mollusk of the family Unionidce 

 taken. It has been found at several places in the Bitter Root river 

 above the junction of this river with the Missoula. At one place a 

 colony was found on a sand bar, when about a peck of live specimens 

 were taken. At another they were found, in March, clinging to the 

 rocks where the water was swift. They were captured by inserting 

 the tip of a switch from a tree between the valves. The shell was 

 closed on the limb, and the specimen pulled from the water. In this 

 way a dozen or so were secured. Pieces of shells have been seen 

 around Flathead lake, but no living specimens taken. In 1900, 

 several dozen were taken in Crow creek, Flathead Indian Reserva- 

 tion. The species is found in all the western mountain streams. At 

 no place is it abundant, and many people who have lived in this 

 country all their lives express surprise at seeing these shells and 

 hearing they are from waters in the State. 



A NEW SPECIES OF LIOMESTTS. 



BY \V. H. DALL. 



Liomesus nassula n. sp. 



Shell solid, white, covered with a pale olive, slightly-hispid perio- 

 stracum, with a rather elevated, subacute spire of seven whorls; 

 suture distinct, not channelled ; apex somewhat eroded with a small 

 blunt top ; surface of the whorls delicately sculptured with fine re- 

 volving threads, four or five to a millimeter, of which about every 

 fourth thread is perceptibly stronger than the other three ; these are 

 crossed by still finer, sharp, elevated, arcuate, incremental lines, 

 along which the hispidity of the periostracum is arranged ; pillar 

 white, solid, twisted, funicular distally ; canal very short, wide ; outer 

 lip thin, simple, with a concave flexuosity behind the periphery; body 

 with a thin white callus. Alt. 42, max. diam. 22, Ion. aperture 17 mm. 



Dredged in 121 fathoms, sand, near the Pribiloff Islands, Bering 

 Sea, by the U. S. S. Albatross. 



