COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 89 



valve the darker. 



The only difference between P. hastatus and this variety is in the 

 relative prominence and abundance of the ribs and riblets forming the 

 fasciculi. In the right valve of the adult van hericius each fascicule con- 

 sists of three nearly equal spiny riblets (the middle riblet of the three 

 being slightly more prominent and spiny), between which and the 

 middle riblet of the adjoining interspace are two small riblets (and 

 sometimes another still smaller pair of intercalaries), while in the adult 

 P. hastatus the fascicular arrangement on the right valve is obscure, 

 there being a central spiny rib with 2 and sometimes 4 faint scaly rib- 

 lets between the major rib and the middle riblet of the interspace. The 

 fasciculi of the left valve of P. hericius are convex, and consist of a 

 central more or less spiny rib, between which and the middle rib of the 

 fascicule of the interspace are about 9 to 12 thread-like scaly riblets; 

 while in P. hastatus there is a high narrow rib with steeply sloping sides, 

 having a top ornamented by numerous tall curved spines; between this 

 rib and the rib running down the interspace are from three to five faint 

 thread-like scaly riblets. (Arnold, 1906, loc. cit.) 



Remarks: The main differences between this subspecies and the 

 typical are the rib structure and the spinose ornamentation. On the left 

 valve of the subspecies the secondary ribs are about half as high as the 

 primary ribs and the latter have spines of only moderate length ; on the 

 typical the secondary ribs are extremely low and narrow, and the pri- 

 mary ribs have very long spines. (The primary ribs of the typical are 

 not high and narrow, as Arnold said above, the very long spines only 

 giving them that appearance.) On the right valve of the subspecies the 

 central riblet of each fascicule has spines of moderate length, which are 

 not greatly longer than those of the adjoining riblets; on the typical 

 the central riblet has spines which are very prominent and much longer 

 than those of the adjoining riblets. The subspecies is seldom oblique, 

 while the typical usually is. 



Young specimens are separable from the young of Hinnites multi- 

 rugosus (Gale) by their more elongate disks, shorter and more oblique 

 posterior auricles, non-divaricating ribs of the right valve, and the 

 absence of concentric lamellae in the interspaces. 



The color range includes deep red to pink, pink-orange, orange, 

 yellow, cream, and white. Radial bands of white or paler shades of the 

 basic color are often present. From three to seven of the major ribs of 

 the left valve are often very pale in color or white, a feature almost 

 never seen in the typical. 



