38 THE NAUTILUS, 
faint, but marked by a recession of the ventral border of the valves, 
which gape but very little and not at all in front; anterior end 
rounded, but smaller than the posterior; ventral border arcuate; 
hinge and pallial sinus much as in the last species, except that the 
sinus is somewhat smaller and less depressed. Lon. 120, alt. 93, 
diam. 50 mm. 
Distribution : San Diego, Hemphill and Cooper. 
This fine and perfectly distinct species appears rare and I have 
seen but two specimens, both from San Diego. 
The preceding species belong to the subgenus Standella as 
adopted by H. and A. Adams, but the following is a true Mactra, 
with the ligament separated from the cartilage pit by a shelly plate. 
Mactra dolabriformis Conrad, 1867, Pl. V. fig. 1. 
Shell much compressed, polished white under a dull brown epi- 
dermis, subequilateral with inconspicuous beaks. It closely resem- 
bles M. faleata Gould (from type) but has higher beaks more cen- 
trally set, the anterior end more attenuated and less truncate, the 
left anterior lateral tooth single and distally more prominent; the 
left cardinal larger and wider ; the posterior adductor scar horizon- 
tally elongate and smaller. Lon. 90, alt. 65, diam. 26 mm. 
Distribution: San Diego, Cala. to Guaymas, Mexico; ‘‘ Panama” 
Conrad. 
This remarkably handsome shell has not unnaturally long been 
confounded with M. falcata, from which the hinge separates it sub- 
generically. 
The true MV. californica of Conrad is a Mactrinula and can at 
once be recognized by its suleate beaks. It reaches 36 mm. in 
length. The MW. planulata is also a small species, resembling DM. 
polynyma in miniature. The northern form generally referred to 
M. falcata is a barely separable variety of M. polynyma which may 
take the name of Alaskana. 
NOTICES OF NEW CHITONS, III. 
BY H. A. BEESBRY. 
Certain rectifications of the previously accepted nomenclature 
have become necessary, and may be made here. 
