MARINE MOLLUSKS — MACGINITIE 191 



H. arctica ranging between 7 and 13.5 mm. in length. Among dozens 

 of specimens (from 3 to 22 mm.) from 477 feet, there were many on 

 which foraminifers were growing and one on which a young Musculus 

 was attached to the byssus. 



Hauls from Eluitkak Pass on Aug. 6, 1948, from 100 feet on Aug. 

 21, 1948, and from 125 feet on Sept. 9, 1948, were unusually rich in 

 Hiatella. A haul from 150 feet on Aug. 23, 1948, not only was very 

 rich, especially in young specimens, but about half of the mass brought 

 up by the dredge was made up of old dead shells of Hiatella. The 

 largest shell (38 mm. long by 16.3 mm. high) came from Eluitkak 

 Pass, and a group of large shells (up to 31 by 14 mm.) came from 10 

 feet in the gravel zone on Sept. 8, 1949. 



Because of their significance as regards growth, selected collecting 

 data are given below: at Eluitkak Pass (Aug. 6, 1948), specimens 2.5 

 mm. long and up; at 184 feet, specimens 2.5 to 18 mm.; at 120 feet 

 (Sept. 15, 1948), 2.5 mm. and up; at 477 feet, 3 to 22 mm.; at 295 

 feet, up to 8 mm.; at 80 and 100 feet (Aug. 21, 1948), 4 mm. and up; 

 at 150 feet (Aug. 23, 1948), 4 mm. and up; at 216 feet, 4 to 12 mm.; 

 at 120 feet (Aug. 8, 1949), 4.5 to 14 mm.; at 217 feet, 4 to 9.5 mm.; at 

 110 feet (Sept. 16, 1949), 5 mm. and up; at 453 feet, 5 to 9 mm.; at 

 185 feet, 5 to 15.5 mm.; and at 175 feet, 6.5 to 19 mm. 



Other material examined: Numerous specimens from the Arctic, 

 and from the Atlantic and Pacific. 



Discussion : Many of the shells from Point Barrow are well shaped 

 (pi. 26, figs. 1-3) (also Oldroyd, 1924, pi. 9, fig. 6) and not distorted 

 as H. arctica often is (Oldroyd, 1924, pi. 51, fig. 4). Young specimens 

 have the characteristic two rows of spines near the anterodorsal 

 margin of each valve, but few retain them very long, their former 

 presence being indicated only by eroded spots along the ridges, and 

 even the latter are sometimes almost obsolete. 



A shell of H. arctica 30 mm. long from Point Barrow is at least 5 

 years old. 



The age-old problem as to whether or not H. arctica and H. rugosa 

 constitute one or two species has received additional argument in 

 favor of two species: Jorgensen (1946) found an oval larval form and a 

 triangular larval form of Hiatella, the former attributed to H. rugosa, 

 the latter to H. arctica. Abbott (1954, p. 453), who lists H. rugosa 

 (Gmelin) as a synonym of H. striata (Fleuriau), states that the eggs of 

 H. arctica are red, while those of H. striata are pinkish cream. 



Distribution: As now conceived, Hiatella arctica ranges in the 

 Pacific area from the Arctic to Panama, and in the Atlantic from the 

 Arctic to the West Indies. 



