72 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull.iog. 



PECTINID^E. 



Genus CAMPTOKECTES (Agassiz) Meek. 



Oamptonectes platessa White. 



PI. ix, Fig. 6. 



Camptonectes platessa White, 1874, Expl. & Sur. West of 100th Meridiau, Prelim. Rept. 

 Invert. Foss., p. 25;— 1876, U. S. Geog. & Gieol. Sur. West 100th Meridian, vol. iv, 

 p. 176, PL 17, Fig. 5a. 



Eevised description: 



" Shell thin, suborbicular in outline; length of hinge-line about equal 

 to one-half the transverse diameter; ears well defined by auricular fur- 

 rows; posterior ear short, flat, its outer margin slightly concave; ante- 

 rior ear moderately large, marked by distinct lines of growth and obscure 

 radiating strire. The anterior ear of the right valve separated from the 

 body portion by a deep, rather narrow, and somewhat angular sinus, 

 the depth of which is equal to about one-half the length of the ear from 

 its outer extremity to the beak. Eadiating stria? of the surface moder- 

 ately fine, increasing in number so rapidly that the direction of the 

 outer ends of those above the middle of the valve is transverse, and 

 farther toward the hinge they are distinctly recurving; the radiating 

 lines crossed by fine concentric stria?, and occasionally by more distinct 

 lines of growth. 



"Height and transverse diameter each about 45 mm . 



" This species somewhat resembles C. bellistriata Meek and ITayden 

 from the Jurassic strata of Dakota; but is proportionally not so broad 

 from front to rear, the ears are proportionally a little longer, and the 

 radiating stria? a little coarser. 



"Locality and position. — Strata of the Cretaceous period; 50 miles 

 north of Camp Apache, and 5 miles west of Mineral Spring, Arizona." 



It also occurs about 350 feet above the base of the Cretaceous in 

 Upper Kanab valley, and at the head of Water-pocket canyon, Utah. 



AVICULID^l. 



Genus AVICULA (Klein) Bruguiere. 



Avicula gastrodes Meek. 



PI. ix, Figs. 7-10. 



Avicula (Oxytoma?) gastrodes Meek, 1873, Aim. Rept. U. S. Gcol. Sur. Terr, for 1872, 



p. 491. 

 Pteria (Oxytoma?) gastrodes White, 1879, Ann. Rept. U. S. Geol. Sur. Terr, for 1877, 



p. 280, Fl. 10, Fig. la. 

 Pteria (Oxytoma) erecta White, 1880, Proc. U. S. Nat. Mus.,.vol. in, p. 157, and vol. 



iv, Figs. 7 and 8 of plate opposite p. 139. 

 Compare Avicula caudigera Zittel, 1866, Bivalven cler Gosaugebilde, PL 12, Figs. 12a 



and 12 b. 



Original description : 



" Shell (as determined from a left valve) attaining a moderately 

 large size, subtrigonal in general outline, rather distinctly convex, and 



