THE CLAM INDUSTRY OF THE UNITED STATES 579 



extruded into the water where they unite and form a swimming embryo which 

 rotates spirally. When the little clam has grown to be about 0.003 inch in diam- 

 eter, an embryonic shell appears. The length of the swimming period varies some- 

 what with the temperature of the water, being, according to Shellford, from 3 

 to 6 days in length. MilUons of these young swimming clams can be found over 

 the clam flats during the reproductive season, which lasts from the middle of June 

 imtil September in waters along the Atlantic Coast south of Cape Cod. A muscu- 

 lar foot, a siphon, and gills appear during the later part of the swimming stage. 

 The projecting pad covered with the swimming ciha, called the "velum," gradu- 

 ally disappears, and the small clam soon settles to the bottom. When it reaches 

 the bottom, a glandular fluid is secreted, which, on being ejected into the water, 

 hardens into a minute thread, called the "byssus"; the tiny clam attaches itself 

 to shells, seaweeds, or pebbles by means of this thread. It does not remain sta- 

 tionary at this stage, but often detaches the byssus and creeps about by means 

 of its foot. When the shell has become about 0.01 inch in length, the young clam 

 begins burrowing into the bottom. When completely buried it spins another byssus 

 and again attaches itself. Occasionally, newly buried clams discard the thread, 

 come to the surface, creep a short distance, and then burrow into the bottom again. 

 When the young clams become about half an inch long, they burrow deeper into 

 the bottom and are believed to remain buried through the rest of their lives. 

 Clams grow from a length of 1 inch to about 3 inches in a single year. 



Venus mercenaria is commonly called "quahog" or "quahaug," "hard clam," 

 "round clam," and in the smaller sizes "cherry stone" and "littleneck"; this clam 

 is common from Cape Cod to Texas. South of New York the quahog is much more 

 abundant than the soft clam and, therefore, is simply called "the clam." Its Ufe 

 history has been studied by Belding (1912) and has been found to be strikingly 

 similar in the early stages to that of Mija arenaria, which has been described 

 above; however, the growth of Venus mercenaria to commercial sizes is decidedly 

 slower. 



The geoduck Panope generosa, found only on the Pacific Coast, is of no com- 

 mercial importance, but is mentioned here because it is the largest of all the 

 clams. Single clams of this species are often more than 8 inches in length and 

 weigh more than 10 pounds. This clam burrows in the mud and sand as deep as 

 3 to 4 feet and sends its siphon to the surface. In most areas it is protected by 

 the prohibition of commercial exploitation and the setting of a low-bag limit 

 for home use. 



Siliqua patula is the most important native Pacific Coast clam and is found on 

 nearly all the sandy beaches from Oregon to Alaska. They obtain their name 

 "razor" from their shape, being rather long and narrow. When disturbed they 

 burrow rapidly into the sand to a depth of 2 or 3 feet, forming large elliptical 

 holes. 



Chemical Composition 



Numerous proximate analyses of clams have been published, but to the authors' 

 knowledge no comprehensive researches on the composition of clams have been 

 carried out. The data (Table 127) concerning the composition of soft and hard 

 clams were taken from Atwater's analyses, as presented by Langworthy. 



