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BULLETIN OF THE BUREAU OF FISHERIES 
and slower to return to productivity when depleted. The importance of this knowl- 
edge for protective regulations as well as for its intrinsic biological interest makes 
desirable the analysis here attempted. 
THE GENUS SILIQUA 
The primary purpose of the present paper is an analysis of the growth data now 
accumulated for the Pacific razor clam. The first question to be considered is that 
of the homogeneity of the material studied. The Pacific razor clam belongs to the 
genus Siliqua of the family Solenidse. This genus includes at least 12 species found 
along the shores of the entire North Pacific from Lower California north to Bering 
Sea and south on the Asiatic side to the Malay Archipelago. The type of the genus 
( Siliqua radiata ) extends into the Indian Ocean and two species are found on the 
North Atlantic coast from the Arctic down to Cape Hatteras. In the initial report 
we briefly discussed the systematic relations of certain of these species (Weymouth, 
McMillin, and Holmes, 1925). More intensive work has convinced us of the validity 
of our former conclusions. Briefly, we consider that there are four species of Siliqua 
on the west coast of North America: S. media, found in Bering Sea and Arctic Ocean; 
S. alta, in Cook Inlet and westward to Bering Sea and Siberia; S. patula, from the 
Aleutian Islands to Pismo, Calif. ; and S. lucida, from Monterey, Calif., to Lower Califor- 
nia. All authorities agree that S. media and S. lucida are distinct species. The present 
view differs from that of Dali (1899) in two respects. S. patula var. nuttallii and typical 
S. patula, which he considers connected by gradiations, we are unable to separate 
on reliable criteria and are forced, therefore, to deny to nuttallii even subspecific rank. 
S. patula var. alta considered by Dali as a variety of S. patula, we find undoubtedly 
entitled to specific rank. A more detailed discussion of these species and their 
relationships is to be presented elsewhere. 
We have arrived at the above conclusions after extensive observations on razor- 
clam beds from San Diego to the Bering Sea. We have dug and handled large 
numbers of animals and have carefully measured over 6,000 shells, the majority of 
these measurements being made under laboratory conditions. In addition to the 
data on form to be presented later, there are differences in the living animal which 
clearly indicate that S. alta represents a distinct species. 
The most notable character in S. alta is the pigmentation. All exposed parts of 
the mantle, siphon, and foot are colored by a chocolate-brown pigment which imme- 
diately distinguishes it from S. patula, which is entirely without this coloration. The 
siphons of S. alta are short and thickly studded with tubercles which become longer 
near the opening. The siphons of S. patula are less closely fused and have a distinct 
tendency to separate near the openings, the exhalant siphon being the longer. They 
also lack the tubercles and do not have as long tentacles about the siphon openings. 
S. alta is found higher on the beach and owing to its short siphon lies nearer the sur- 
face. These differences and the distinctive pigmentation in S. alta make it possible 
for the commercial clam diggers to recognize these two species readily and to avoid 
taking S. alta. 
DIFFERENTIAL GROWTH RATIOS IN SILIQUA PATULA AND S. ALTA 
Since the shape of the shell is an important specific character in the genus 
Siliqua, an analysis of the variations in form of the material studied was necessary. 
Accordingly, not only the length but also, in many cases, the width and the distance 
