RECENT PECTENS. 139 



ment as to their ocjuivalence, but from the large aniouut of material examined it is 

 eiearly evident that the three are very closely related. /'. pivlhami averages smaller 

 than the other two and has usually onlj- four radials on the right anterior ear, while 

 P. ped roil mix is the largest of the group and is generally nuich more prominently 

 undulated than the others. The three speeies are so niueh alike, at any rate, that 

 with the usually poor state of preservation of the Miocene fossil forms it would be 

 impossible to make anj' definite distinctions in !>9 per cent of the cases that have fallen 

 under the observation of the writer. This being true, it is (juite evident that the two 

 forms, /*. pt'driiuiiKff and /*. iK'rklniiii!. wiiich heretofore have always been considered 

 diagnostic species of the Miocene, at once lose their value as agents of correlation. 

 A further study of well-preserved fossil material, if any is ever obtained, will undoubt- 

 edly tend to make clear the relations existing lietween the members of this verv 

 interesting little group. 



The type of P. nindolj>h! (U. S. N. M., l(»774it) was dredged by the U. S. Fish 

 Commission steamer A/hutruss oS Destruction Island. Washington, in oK! fathoms, 

 bottom temperature, 38" F. 



KANr.E. 



Living. Bering Sea to West Mexico, in 225 to l.uu.> fathoms (U. S. Fish 

 Commission.) 



Pecten (Pseudamusium) kandolphi Dall var. tillamookensis n. var. 



PI. XLVIII, tias. .HandSo. 



Descvi ptinn. — Shell resembling P. nutdoljihl in outline and general charac- 

 teristics. Disk ornamented by numerous more or less lirominent, fine, radiating 

 ridges, microscopic radiating striw, and incremental lines of varying prominence. 

 The radiating ridges are narrow and thread-like, and appear to })e more prominent 

 anteiiorly and near the lines of interrupted growth; the ribs are afiected similarly 

 to the disk l)v the interruptions in growth. The microscopic striaj cover the 

 whole surface of the disk and rilis and in a general way radiate from the umbo, 

 but are seldom parallel to the ribs; on the portion of the disk and ear posterior 

 to the umbo the stri;e are perpendicular to the lines of growth and are thus 

 nearly parallel and not I'adiating. The right anterior ear has from B to 12 

 prominentl}' imliricated radials. 



Dimensions. — Alt. 3n nun.; long. oU mm.; hinge line 17 nun.; diameter 7 nuu. 



This variety appears to combine some of the characters of P. /yincoiivi'/'eiis/s 

 with d\ nuidolplii, having the prominent radial sculpture of the former and the 

 relatively large, undulated disk of the latter; the ears in P. var. tiUainoohenni^ 

 are sculptured more nearly like the former, having from 1 to ti more radials 

 than /'. rundolplii. 



This variety general Ij' occurs in deeper water, along the northwestern coast, 

 than the typical form, being found at depths of from 400 to S()() fathoms. 



The type, U. S. N. M. 150233, is from off Tillamook Bay, Oregon, at 

 U. S. F. C. Sta. 3316, at a depth of 78ti fathoms. 



KANUE. 



Living. From north of Unalaska, 351 fathoms, to oti' Tillamook Bay. 736 

 fathoms. (U. S. Fish Commission.) 



