— 15 — 



Shell very thin and fragile, over twice as long as wide and gapine 

 about equally at both ends, with conspicuous glossy periostra- 

 cum, a marked rib on the interior of each valve extending from 

 the umbo toward the free margin; found in clear sand on open 

 beaches. 



Razor clams Siliqua 



p. 50 ; pi. 15 , fig. 4 



Fic. 1,^. Siliqua. On«-haIt" natural 



ff. Shell strikingly elongated (length three or more times the breadth), 

 with hinge margin and free margin parallel or nearly so, gaping 

 about equally at both ends ; animal moving freely up and down a 

 permanent burrow. 



Jackknife clams 



g. Umbo centi-al : siphons sepaiate, long. 



Tagclus calif ornia)tus 



p. 48; pi. 15 , fig. 1 



gg. Umbo at extreme anterior end, siphons united. 



Solen 



h. Animal of moderate size ; shell slightly curved, about 4 times as 

 long as wide, with yellowish periostracum ; foot with dark 

 pigment. 



S. sicarius 



p. 50 ; pi. 15 , fig. 2 



hh. Animal small ; shell straight, about 5 times as long as wide, with 

 slight transparent periostracum through which the flesh color 

 of the shell usually shows ; foot with little or no pigment. 

 S. rosaccus 



p. 50 ; pi. 15 , fig. 3 

 I 



Fig. 16. Schizothaenis nuttaUL One-half 

 natural size. 



ee. Ligament internal, shell not strikingly elongated, without parallel mar- 

 gins ; siphons with heavy dark epidermis, 

 f. Lower edge of pallial sinus united with pallial line ; cartilage pits equal 

 in the two valves ; retracted siphons projecting beyond shell, tip 

 with a pair of plates ; umbo nearer the anterior end of the shell. 

 Gaper Schizothaerus nuttalli 



p. 54; pi. 16 , fig. 3 



