GENUS PECTEN Ml'LLER. iS 



smaller and more rounded on the left valve: concentric sculpture inconspicuous; 

 radial stria» absent or obsolete, ears subequal; valves nearly e<[uilateral. 



To this oroup belonu- the following Pectens: cootietixis, caiirlniix, dilh-ri, 

 healeyi^ inoeni, purMiinacnsis^ jiropatulns, and tirnicrt. 



Subgenus Kodipecten Dall. 1898. 



Type P. nodosuii Linne. 



Shell like Lyropectcn. but the ribs intermittently nodose, with more or less 

 prominent hollow nodes or bulhv; radial striation pronounced; ears unequal, the 

 posterior smaller, the valves often more or less oblique; imbricate surface layer 

 sometimes very marked. {P. wattfi is a connecting link between this sufigenus 

 and the typical C/i/aiiii/x.) 



The only representatives of this group are J', si/httx/oxnx and /'. reatchH. 



Subgenus Chlamys Bolten, 1798. 



Type /'. islandiciis Miiller. 



Valves moderately inflated, subequal. similar, oblique, or with unequal ears, 

 the posterior smaller; Cuiiipfoncetes striation and imbricate surface layer usually 

 present; shell usually solid and opaque; byssal notch and ctenolium present. 



Under this subgenus are grouped the following Pectens: hartfo-lii, hclUhnnd- 

 latus, h'cmneri^ calliiisi. fucanus, hainlini, hmtatiis and vars. herickm, alhidus, 

 hlndsii, navarchvs and strategus, idandicus, jm'dani, kindest, latiauritus and vars. 

 cerritenHis, delosi, f\icicoJm and monotiineris^ lawsoni, nuttein, opuntia, pnnne.leei., 

 proavus, sespeensLi\ and its variety kydei\ waxhlmrnel, waffsi. and its variety itwrtini. 



Subgenus Lyropecten Conrad, 1862. 



Type P. estrellanus Conrad. 



Shell resembling Pet-ten s. s. , but with both valves convex; usually of large 

 size, heavj', and with radial striation and minute concentric imbrication; ribs entire, 

 and not dichotomous; valves equilateral and sometimes more or less undulated in 

 the vicinity of the umbones. 



This group includes the following Pectens: Ashleyi, imnersi, crahsicardo and 

 its variety hamiltoni, estrellamis and its varieties cataUnee> and tei'minm, magnolia, 

 miguelensis, perrinl, and vaughani. 



Subgenus ^Equipecten Fischer. 1887. 



Type /*. operculartx Linne. 



Shell thin, orbicular, with subequal inflated valves, usually equilateral, with 

 uniform, well-marked radial, not dichotomous, ribs and tineh' iml)ricate i-adial 

 striation; ears subequal; valves internally Urate on the edges of the grooves 

 corresponding to the external ribs; Catii]>toiieffe>< striation present, but usually 

 obscured by the radial sculpture; ctenolium and byssal notch obvious. 



The single repi'esentative of this group is /'. pahneri. 

 17260— No. 47— Oti 4 



