174 PROCEEDINGS OF THE NATIONAL MUSEUM vol. loo 



fine concentric incremental lines, with about 6 growth-cessation lines. 

 Teeth (as for the genus: 2 in right valve, none in left) large for size 

 of shell, subequal. Muscle scars rounded, pallial line even. 



Dimensions: Holotype, length 2.3 mm.; height, 1.9 mm.; depth, 

 1.4 mm. 



Type locality: About 12.1 miles off Point Barrow base, Alaska. 

 Depth, 741 feet. Bottom, mud (haul containing mostly terebellid 

 worm tubes, chiefly Pista maculata). Collected by G. E. MacGinitie, 

 Aug. 17, 1949. 



Kepository: Holotype in U. S. National Museum, No. 610302. 



Other localities: Three specimens (labeled Montacuta dawsoni; 

 USNM 170490) from Greenland. 



Remarks: The resilium of this specimen is missing. This species 

 belongs near M. tumida. It is more tumid and more trigonal than the 

 latter, and the posterior tooth is not so elongate as that of M. tumida. 

 It is named in honor of Mr. Pete Sovalik, an Eskimo assistant at the 

 Arctic Research Laboratory. 



Genus Montacuta Turton, 1822 



Montacuta planata (Dall, 1885) 



Plate 20, figures 1, 3-7, 9-11 



Unnamed bivalve No. 7, MoUer, 1842a, p. 24. 



Montacuta elvata Morch, in Jones, 1875, p. 131 (not of Stimpson, 1851). 



Montacuta molleri "Holboll" Morch, in Jones, 1875, p. 131; in Rink, 1877, p. 



441 (name only). 

 Montacuta ferruginosa var. gronlandica Morch, in Rink, 1857, p. 91 [specimen 



No. 164] (fide Posselt, 1898, p. 75). 

 Tellimya planata Dall, in Krause, 1885a, vol. 51, p. 34, pi. 3, figs. 6a-d. 

 Montacuta molleri Posselt, 1898, vol. 23, p. 74. 

 Mysella planata Dall, 1899, p. 892, pi. 88, fig. 12. 

 Mysella molleri Dall, 1899, p. 891, pi. 88, fig. 14. 

 Rochefortia planata Dall, 1921, p. 37.— Oldroyd, 1924, p. 132. 



Eight fairly typical living specimens were dredged: 1 (1.9 mm. long 

 by 1.4 mm. high) from 216 feet; 1 (4.4 by 3.3 mm.) from 328 feet; 



1 (2.8 by 2.1 mm.) from 341 feet; 1 (3.3 by 2.4 mm.) from 477 feet; 

 and 4 (1.5 by 1.1 mm., 1.8 by 1.4 mm., 2.2 by 1.6 mm., and 2.8 by 



2 mm.) from 741 feet. 



Four other living specimens, possibly variants of M. planata, were 

 dredged: 3 (6.9 by 4.9, 3.1 by 2.4, and 1.5 by 1.3 mm.) from 477 feet 

 and 1 (1.8 by 1.4 mm.) from 741 feet. 



Other material examined: The type (1 right valve) and cotypes 

 (USNM 159303) of Ball's Tellimya planata from Plover Bay, Siberia 

 (see pi. 20, fig. 3); his figured type (USNM 159310) from the Shuma- 

 gins (pi. 20, fig. 6) ; and approximately 30 specimens (including dead 

 shells) from localities ranging from Icy Cape (1 specimen), Nunivak 



