NO. 1139. DKI-'.l'-WATER MOLLUSCAVKRRILL AXH lifsll. 829 



LYROPECTEN Conrad, 1867. 



l.irojxTlen of several later authors. 



I.yropedtn ( 'ONRAD, 1867. VERIMI.I., Trans. ( 'nun. Arad., X, pp. ii:>, M!>, ll. 1897. 



Type. Lyropecten noflosns (Linnaeus). 



Shell large and strong, corrugated, with large, fluted, and usually 

 nodose, primary radial ribs, which do not increase in number, and 

 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 denned 

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

 Pallium. 



PROPEAMUSIUM Gregorio, 1883. 



I'rojH'amiisiinn (subgenus) DALL, Bull. Mas. Comp. Zool., XII, p. 210, 1886. 

 FISCHER, 18X7. (genus) VKKUILL, Trans. Conn. Acad., X, pp. 61, 90, 92, pi. 

 xx, figs. 5-9, 1897. 



Type. Propeamusium inequisculpta (Tiberi) = Propeamusium fenes- 

 tratiim (Forbes). 



This group is allied to Amnsium. It includes small, mostly deep-sea 

 species, with thin, rounded 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 Cyclo- 

 pecten. 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 Amusmm 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 obvious 

 difference in the shells is in the presence of internal ribs. 



PALLIOLUM Monterosato, 1884. 



I'nllinliun (submenus or section) VKKKILL, Trans. Conn. Acad., X, pp. 65,90,91, 

 pi. xvm, tigs. 6-1-1,1897. 



Types cited. Palliolwm testce (Bivona) and Palliolum rilrnun- (Chem- 

 nitz). 



This group is separated from Pseudamusium H. and A. Adams, and 

 can scarcely be distinguished from Camptonectes by any known char- 

 acters. 



The two species named by its author as types agree in having thin, 

 rounded, nearly equivalved shells, with the posterior auricle poorly 

 developed, and with tine camptonectes sculpture on both valves, with 

 small radial riblets, and usually with rows of small scales. The mar- 

 gins are plain and come evenly together, without flattening. 



