806 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxiii. 



This is ;i well-marked g-roup, belonging in the warmer seas and 

 having a very elegant type of sculpture. 



Subgenus Miltha H. and A. Adams. This is Miltha H. and A. Adams, 

 1857, and Milthea Meek, 1870. The typ(» is Lncina ohildreni Gray, 

 1825, as Tellina. 



This group is solid, compressed, concentrically striate, with a con- 

 spicuous periostracum, narrow impressed lunule, inconspicuous dorsal 

 areas, deeply inset but not internal ligament and resilium and entire 

 margins. It is divisible into two sections: 



Miltha s. s. Hinge with two clean-cut cardinal teeth in each valve, 

 the inner pair ))ilid, the laterals absent or obsolete. 



Pseudomiltha Fischer, 1885. Type, L. (ilgantea Deshayes, Eocene 

 of Paris. 



Shell much like M/ltlia^ but with the hinge teeth wholly obsolete. 



This type goes back to tTie beginnings of the Tertiary and includes 

 some of the largest lucinoid forms known; one, the Luc'ina megameris 

 Dall, of the Jamaican Oligocene, reaches a length of some 10 inches. 



Subgenus Lucinoma Dall, 1901. Type, Lucina filom Stimpson. 



Shell usually large, lentiform, white, with a conspicuous periostra- 

 cum, concentrically lamellose or striated; the cardinal teeth developed, 

 the inner pair usually bitid; the laterals obsolete or absent, the inner 

 margins entire. 



This is a well-marked group with extensive geographical and geo- 

 logical distribution, inhabiting preferably cold waters and frequently 

 abj^ssal depths. 



Subgenus Callucina Dall, 1901. Type, Lucina radians Conrad. 



Shell Dosinoid, concentrically filose, sometimes with feeble radial 

 sculpture; the dorsal areas o])Solete; the lunule small, comprised chiefl}" 

 in one valve and litting into a recess in the opposite valve; hinge with 

 one cardinal in each valve, the other teeth feeble or absent; inner mar- 

 gins crenulate. 



The L. concentrlca Reeve is also a mem))(n- of this group, wliich 

 comprises the typical section, as above; and 



Section Eplluclna Dall, 1901. Type, Luelva CaJlfornica Conrad. 



Shell veneriform, convex, all the hinge teeth developed, inner mar- 

 gins entire; otherwise like Callucina. 



Subgenus Parvilucina Dall, 1901. 



Shell small, plump, often inecjuilateral; sculpture more or less retic- 

 ulate but not nuiricate, teeth small, l)ut all usuall}^ present. 



Section Parvilucina s. s. TVpe, Lucina tiuvlsculpta Carpenter. 



Dorsal areas obscure or obsolete, sculpture feeble. 



Section Bellucina. Dall, 1901. Type, Parvilucina eucosmia Dall, 

 1901 {■==== Lucina plsniii Reeve, 1850, not Sowerby, 1887, nor 

 d'Orbigny, 1841, nor Philippi, 1850). 



Dorsal areas and sculpture strong. 



