HIATELLIDAE 45 3 



the dorsal and ventral margins usually parallel to each other. A posterior 

 gape may be present. Beaks close together, about % back from the anterior 

 end. Just behind them is a conspicuous, bean-shaped, external ligament. 

 Shell chalky, white and with coarse, irregular growth lines. Periostracum 

 gray, thin and usually flakes oif in dried specimens. With a weak or fairly 

 strong radial rib at the posterior end. The rib may be scaled. Common in 

 cold water. This is H. rugosa Linne and pholadis Linne. 



■ Hiatella striata Fleuriau {H. galUcana Lamarck and rugosa of some 

 authors) is almost indistinguishable in the adult form from arctic a. The 

 young, however, in striata do not have the two radial spinose ribs. This 

 species breeds in winter, while arctica breeds in summer. The eggs are pinkish 

 cream, while those of arctica are red. It nearly always bores into stone. 



Genus Cyrtodaria Daudin 1799 

 Cyrtodaria siliqiia Spengler Northern Propeller Clam 



Labrador to Rhode Island. 



2 to 3 inches in length, about H as high. Gapes at both ends, but more 

 so posteriorly where the large siphonal snout projects out about an inch. 

 Beaks hardly noticeable, placed slightly toward the anterior end. The 

 strong, wide ligament is external at the very anterior end of the dorsal mar- 

 gin. Shell chalky, white with a bluish tint. The valves are thick-shelled, with 

 a coarse callus inside. The valves are slightly twisted in propeller fashion. 

 Hinge a simple bar with a fairly large bulbous swelling under the ligament. 

 In life, the periostracum is light-brown, glossy, smooth and covers the en- 

 tire exterior. Dried valves soon lose the flaky, blackened periostracum. 

 Moderately common offshore down to 90 fathoms. On occasion, found in 

 fish stomachs. 



A similar species, Cyrtodaria kurriana Dunker, is found in arctic waters 

 along the shores at low tide. It is 3 times as long as high, hardly twisted 

 and rarely exceeds 1% inches in length. Uncommon in collections. 



Genus Fanomya Gray 1857 

 Panomya arctica Lamarck Arctic Rough Mya 



Arctic Seas to Chesapeake Bay. 



2 to 3 inches in length, about Y2 as high, squarish in outline. Looks 

 somewhat hke a misshapen Alya, but lacks teeth and a chondrophore in the 

 hinge, and has a coarse, flaky, light-brown periostracum. Characterized by 

 oblong or oval, sunk-in muscle and pallial line scars. There are 2 poorly de- 



