932 ASTARTIDA. 
Mriunerta, Dall, 1881. 
Etym.—In honor of the late Dr. J. W. Milner, of the U. 8. 
Fish Commission. Syn.—Ceropsis, Dall, 1871. 
Distr.— M. minima, Dall. Nestling in Haliotis, California. 
Shell small, ribbed or sculptured; with a A-shaped cardinal 
tooth in the right valve; left valve with a stout anterior and 
slender posterior cardinal tooth, diverging, and a very slight 
groove in the posterior margin; no lateral teeth in either valve, 
and no groove in the right valve; umbones almost postericr, 
general form trapezoidal. 
MyviticarprA, Blainv., 1824. 
Distr.—24 sp. Universal. MM. variegata, Brug. (cxxiii, 69). 
Shell elongated, very inequilateral, with squamous radiating 
ribs; hinge with an anterior triangular cardinal tooth ; posterior 
cardinal tooth double in the left valve; no anterior laterals. 
Foot rounded, grooved, byssiferous. 
AZARELLA, Gray, 1852. (Beguina, Bolten, 1798.) Shell com- 
pressed, margins rounded, striated; hinge elongated, submar- 
ginal, without lateral teeth. J/. semiorbiculata, Linn. (exxiii, 
Os v1). 
GLANS, Muhlfeldt, 1811. Shell trapezoidal, with radiating ribs. 
M. trapezia, Brug. 
THECALIA, H. and A. Adams, 1855. Shell oblong, radiately 
ribbed ; interiorly with a remarkable cup-like inflection of the 
ventral margin of each valve, resembling the cup of a Calyptriea. 
M. concamerata, Chemn. (exxii, 49). 
PALMOCARDITA, Con., 1867. Shell elongately trapezoid, inequi- 
lateral, moderately inflated, radiately ribbed; hinge with two 
blunt cardinal teeth and one posterior lateral tooth in each valve. 
Conrad proposed this group for the Triassic Cardium austriacum, 
Hauer, but the better known Cassian Cardita crenata, Munst. 
(exxii, 50,51), may rather be considered as the type. These 
cretaceous Mytilicardiz mostly differ from the recent species by 
the want of an anterior insinuation of the ventral margin, where in 
true Mytilicardiz there should be a small gape; the posterior 
cardinal is also less elongated in the fossil forms. 
CARDITAMERA, Conrad, 1838. 
Syn.—Lazaria, Gray, 1853. 
Disir.—6 sp. W. Coast N. America, W. Indies, Madagascar. 
Fossil. Miocene; U.S. C..pectunculus, Brug. (exxiii, 72). 
Shell transverse, oblong, inequilateral, beaks subanterior, radi- 
ately ribbed; hinge with two cardinal and two lateral diverging 
teeth in each valve, the posterior teeth being in each case much 
elongated, the anterior short and more or less pointed, sub- 
lunular. 
