RECE^fT PECTENS. 137 



adult, soinirated l.v narrower .•hiuineled interspaces, eaeb -?ith a mesial thread; all 

 crossed l)y hunellose. concentric, rather sparsely distributed elevated lines; submar- 

 gins and" ears closely radially threaded with imbricated threads. Both valves 



similarlv sculptured." 



Dimens!ons.—A\t. 47.5 mm.; long, b?, mm.; diameter al)out '20 mm. 



This species is easily distinguishable by its flat, orbicular disk and peculiar 

 sculpture. It is known only in the recent faunas, and is found near the head of the 

 Gulf of California, from whence the type and several other valves were obtained by 

 Dr. E. Palmer some years ago. 



KANXiE. 



Living. Near head of Oulf of California (H I'almer). 



Pkcten (Plauioctenium) paucicostatus Carpenter. 



Fl. XXXIX, fig^. S, ^■^ll, and 4. 



1863. Pcclen paacicustatas Carpenter, Brit, .\ssii. Kept., 1863, i>. 645. 



1865. Pecten jiaucicostatus Carpenter, Ann. and Mag. Nat. Hist., 3d-i-er., vol. 15, 1865, p. 179. 

 1888. Pectm paucicostatus Carpenter, Kiister and Kobelt, Conch.-Cab., vol. 17, pt. 2, Spondylus und 

 Pecten, no. 9, p. 281. 



Description.— HheW averaging about 35 millimeters in altitude, longer than high, 

 subequivalve. moderatelv ventricose; thick-shelled; margins smooth. Right valve 

 subequilateral, slightlv more ventricose than the left; ribs 12 to U, prominent, 

 convex-topped, subangular; interspaces slightly wider than the ribs, somewhat 

 rounded; incremental sculpture fine and regular, not looped; hinge line about fiye- 

 .sevenths length of disk; ears moderately prominent; anterior ear with aljout five 

 prominent radiating ridges and munerous incremental lines; byssal notch prominent; 

 posterior ear similar to anterior in sculpture, except that it is not quite so pronounced 

 as in the latter. Left valve with prominent subangular ribs, slightly narrower than 

 tho.se of the right valve; interspaces correspondingly wider and flat-bottomed; ears 

 similarlv sculptured to those of right valve. 



Diw,n><!i»,s. -Alt. 34.5 mm. ; long. 37 mm. ; liinge line 25 mm. ; diameter 13 mm. 



The specimen described is No. 15ti43, U. S. N. M. It is dark brown in color, 

 with no patterns or t)lotches. This species is distinguishable from P. latianrdus 

 and varieties bv its much heavier shell, dark uniform color, sliorter hinge line, and 

 fine uniform concentric lines. The type is labeled ''Santa Barbara" by Jewctt, but 

 is unquestionablv from the Gulf of California, as no species with its characteristics 

 are known outside of the tropical fauna. Besides, Jewett was known to be quite 

 careless regarding the localities of his specimens. 



R.VNGE. 



Living. Gulf of California (Jewett, Stearns). 



