232 ASTARTIB^. 



MiLNERTA, Dall, 1881. 



Etym.—ln honor of the late Dr. J. W. Milner, of the U. S. 

 Fish Commission. /Sy«.— Ceropsis, Dall, 1871. 



Distr. — M. minima^ Dall. Nestling in Haliotis, California. 



Shell small, ribbed or sculptured ; with a A-sliaped 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 posterior, 

 general form trapezoidal. 



Mytiltcardia, Blainv., 1824. 



Distr. — 24 sp. Universal. M. 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, 1198.) Shell com- 

 pressed, margins rovmded, striated ; hinge elongated, submar- 

 ginal, without lateral teeth. M. semiorbiculata, Linn, (cxxiii, 

 10,11). 



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 Calyptrsea. 

 M. concamerata, Chemn. (cxxii, 49). 



PAL^ocARDiTA, 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 6'a7'diu7?i austriacum, 

 Hauer, but the better known Cassian Gardita crenata, Miinst. 

 (cxxii, 50, 51), may rather be considered as the t^^De. These 

 cretaceous Mytilicardise mostly difler from the recent species by 

 the want of an anterior insinuation of the ventral margin, where in 

 true Mytilieardiae there should be a small gape ; the posterior 

 cardinal is also less' elongated in the fossil forms. 



Carditamera, Conrad, 1838. 



Syn. — Lazaria, Gray, 1853. 



Distr. — 6 sp. W. Coast N. America, W. Indies, Madagascar. 

 Fossil. Miocene ; U. S. G. pectunculus, Brug. (cxxiii, 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. 



