220 WEST AMERICAN SHELLS STEARNS. 



The subgeneric distinctions made in the Venericardia group by Con- 

 rad are simply frivolous aud uucalled for. The intimate relationship of 

 forms like borealis, ventricosa, tridentataandbarbarensis, are apparent ata 

 glance, and the differences upon which these distinctions are based, as 

 in Cyclocardia and Pleuromeris, are of no greater than specific value. It 

 is highly probable that this criticism might with propriety be extended 

 to other related genera, which have been admitted and perpetuated in 

 conchological literature. 



Suborder Lucinacea. 

 Family Lucinid^. 



Genus LUCINA Brugniiire. 



Lucina aequizonata sp. iiov. 



Plate XVII, Figs. 3, 4. 



Shell moderately convex, dull white chalky where eroded ;' epidermis 

 of a dull dingy light yellowish tinge, finely wrinkled in old specimens, 

 and inclined to be deciduous and slightly flaky or ragged; in young 

 shells, translucent, shiny, and nearly colorless. Valves transversely 

 ovate, being broader than high; the posterior side is abruptly squarish, 

 and the dorsal line slants gradually from the umbones; on the anterior 

 side the dorsal outline is moderately concavely curved away from the 

 beaks, and in young and perfect specimens a very slight angulated 

 pinch may be seen extending from the lunule to the anterior edge of the 

 valves. The beaks or umbones are small, inclined towards the lunule ; 

 thelunuleisquite narrow, attenuately lanceolate andelongated. Surface 

 of valves transversed with fine concentric growth lines, and prominent 

 rather regularly spaced thread-like ridges. Hinge line curved and show- 

 ing two diverging cardinal teeth in each valve ; the anterior one in the 

 left valve, and the posterior one in the right valve, notched or partially 

 cloven. Elongated, tuberculoid lateral teeth in both valves at extreme 

 limit of dorsal or hinge line. Dimensions: From beaks to ventral mar- 

 gin, 37.50'"'" ; from anterior to posterior edges of valves, 46.'J5""". Indi- 

 viduals otherwise of same dimensions vary much in rotundity; two ex- 

 amples measure, the one 21.75'"'", the other 17.75"™ diameter or thick- 

 ness. 



Habitat. — Off Santa Barbara Islands, California, in green mud in 

 270 fathoms May 8, 1888, U. S. Fish Commission, Steamer Albatross, 

 common (filty specimens), Museum No. 104044. 



In Stimpson's Lucina Jilosa (Museum number 92679, see Plate xvii, 

 figures 5, G), there are no lateral teeth, and the valves are more nearly 

 orbicular in outline. In L. borealis, the European form, to which Car- 

 penter assigned the specimens dredged by Dr. Cooper near the islands 

 in the Santa Barbara Channel (30 to 120 fathoms), there is an incon- 

 spicuous anterior lateral discernible in the right valve, but no posterior 

 lateral. 



