MARINE MOLLUSKS — MACGINITIE 189 



Family Hiatellidae 



Genus Panomya H. and A. Adams, 1858 

 Panomya arctica (Lamarck, 1818) 



Plate 19, figure 1; Plate 25, figures 6, 8 



Glycimeris arctica Lamarck, 1818, vol. 5, p. 458; 1835, vol. 6, p. 70. 



Panopaea arctica Gould, 1841, p. 37, fig. 27; 1870, p. 51, fig. 378. 



Panomya turgida Dall, 1916, p. 416; 1921, p. 54, pi. 2, fig. 1. 



Panomya ampla Oldroyd, 1924, pi. 10, fig. 3.— Morris, 1952, p. 93, pi. 16, fig. 10.— 



Kira, 1954, p. 123, pi. 61, fig. 17. 

 Panope (Panomya) ampla Grant and Gale, 1931, p. 426, pi. 21, figs. 10a, b. 

 Panomya arctica Morris, 1951, p. 91, pi. 43, fig. 16. 



Three left valves of this species, ranging from 73 to 78 mm. in 

 length, were dredged at 522 feet. 



Other material examined: The figured type of P. arctica, the 

 figured type of P. turgida; specimens of P. arctica from Scotland, fos- 

 sils from Sicily, several specimens from localities ranging from Gaspe 

 Bay, Quebec, to Chesapeake Bay; and 3 specimens of P. turgida from 

 Unimak Pass, Unalaska Island, and Port Levasheff . 



Discussion: Typically, the anterior end of P. arctica (pi. 25, figs. 

 6, 8) is rounded (instead of being tapered as in P. ampla) and the 

 posterior end is obliquely truncate in such a manner that the ventral 

 margin extends farther posteriorly than does the dorsal margin (pi. 

 19, fig. l;pl. 25, figs. 6, 8; also see Dall, 1921, pi. 2, fig. 1). The degree 

 of the posterior extension is highly variable, ranging from slight (see 

 Oldroyd, 1924, pi. 10, fig. 3) to marked. In one specimen from Una- 

 laska and one from Port Levasheff the dorsal margin extends as far as 

 the ventral, and in the latter shell the anterior end is somewhat 

 tapered (as in Oldroyd, 1924, pi. 10, fig. 3) ; but in none of these speci- 

 mens does the dorsal margin extend beyond the ventral as is the case in 

 P. ampla. I could detect no difference between specimens of P. arctica 

 and P. turgida. There are specimens of P. arctica from our east coast 

 that are practically identical with specimens called P. turgida from 

 our west coast. 



Distribution: Point Barrow south and east to Unalaska and the 

 Shumagins; in the Atlantic area from the Arctic Ocean to Chesapeake 

 Bay, the British Isles, and north of Europe. The specimens from 

 Point Barrow extend the range into the Pacific area of the Arctic. 



Panomya ampla Dall, 1898 



Plate 25, figure 7 



Mya truncata Middendorff, 1851, pi. 25, fig. 13. 



Panomya ampla Dall, 1898, p. 833: 1902, p. 560, pi. 40, figs. 3, 4. 



