64 A. E. Verrill — Study of the family PectinidcB. 



with coarsely scalloped margins. Valves somewhat unequal. Auri- 

 cles of medium size, unequal. Hinge-plate with several, usually three, 

 oblique, divergent ribs on each end. This is one of the best defined 

 groups, and may be regarded as of generic value. It is allied to 

 Pallium. 



Several species occur in the American tertiary deposits. L. nodosus 

 occurs at Florida and in the West Indies. X. subnodosus is from 

 the tropical regions of the Pacific coast of America. Z,. cor allino ides 

 (D'Orb.) is from West Africa and the Canary Islands; L. noduliferus 

 (Sow.) is from East Africa. 



Euchondria Meek, 1874. Type, E. negleeta (Geioitz). 



Euchondria Meek, Amer. Journ. Sci., 3d ser., vol. vii, p. 443, 1874; Hall,. Pal. of 

 New York, v, Pt. 1, sec. II, Introduction, p. Ixii, figs. 4, 5, 1885. 



The shell of the type of this genus has nearly the form of Cyclo- 

 pecten and Propea^nusium, to which it seems closely allied. The 

 auricles are well-developed and angular, subequal. The body of the 

 shell is well rounded ; the sculpture is slight, consisting of concentric 

 lines on the bodj'', but there are radial ridges on the auricles. There 

 is a distinct triangular chondrophore, situated slightly one side of 

 the beak. The hinge-plate has a row of very small, close, incised, 

 transverse pits or grooves on each end. These seem to correspond 

 closely with the grooves, alternating with denticles, on many modern 

 species, and not with ligament pits. 



Carboniferous of Illinois. 



Propeam.usiuni Gregorio, 1883. Type, P. inequisculjita Tib. = P. fenesiratum- 



Forbes. 



Proj^emnusium {subgenus) Ball, Bull. Mus. Comp. Zool., xii, p. 210, 1886; Fischer, 



1887. 



Plate XX. figs. 5-9. 



This group is a subdivision of Amusium. It includes small, mostly 

 deep-sea species, with rounded thin shells, having the valves unequal 

 in size and sculpture ; the lower and flatter one is concentrically 

 grooved, and usually turns up at the thin margin to meet the upper 

 valve, as in Cyclopecten. The upper valve may be cancellated or 

 radially sculptured. When full grown there are several well-formed, 

 raised, internal ribs ; these may be absent in the young. 



This division differs from Amusium in the sculpture of the valves 

 and in having the auricles and byssal notch well-developed. 



The species closely resemble those of Cyclopecten ; the only ob- 

 vious difference in the shell consists in the internal ribs. The species 



