H. Doc. 129. 15 



MYTILUS, Lin. 



32. M. PEDROANUS, Con. , pi. , fig. 40. Oblong-subovate, ventricose, 

 dorsal line undulated medially, angle rounded; beak projecting slightly 

 beyond the basal margin ; posterior extremity rounded ; basal margin 

 rectilinear. 



'Locality, San Pedro. Recent formation. 



PECTEN, Lin. 



33. P. DESERTI, Con., pi. , fig. 41. Suborbicular, both valves 

 convex; ribs about 23, rounded, somewhat flattened toward the base, 

 about as wide as the interstices ; in the lower valve much wider than 

 the interstices, and the valve more convex than the opposite one ; ears 

 equal in the upper valve ; left ear of lower valve extended downwards 

 and very obliquely striated; cartilage pit profound; a submarginal 

 channel parallel with the upper margin. 



Locality, Carrizo creek, Colorado desert. Miocene. 



ANOMIA, Lin. 



34. A. SUBCOSTATA, Con., pi. , fig. 34. Obtusely ovate, thick in 

 substance, umbo of larger valve ventricose, hinge thickened ; surface 

 of this valve obtusely undulated concentrically and marked with 

 waved, wrinkled, very irregular interrupted ribs, not much raised 

 except toward the base, where they are larger and somewhat tuberculi- 

 form, upper valve entire, or with obsolete radii toward the base. 



Locality. Carrizo creek, Colorado desert. Miocene. 

 Allied to A. Ruffinl of the Virginia Miocene, but thicker, less ex- 

 panded, and with the radii more numerous and more rib-like. 



OSTREA, Lin. 



35. o. VESPERTINA, Con., pi. , figs. 36, 37, 38. Ovate, subfalcate, 

 lower valve plicated or ribbed more or less profoundly; hinge long and 

 wide, sharp and somewhat pointed ; ligament cavity wide, profound, 

 minutely wrinkled ; margins abrupt ; cavity not very deep ; muscular 

 impression large, impressed ; upper valve flat, irregular, plicated on 

 the margin; a submarginal furrow, slightly impressed, crenulated 

 nearly to its basal curve, profoundly crenulated towards the hinge. 



Locality. Carrizo creek. Miocene. 



0. vespertina. Con. Jour. Acad. Nat. Sc., new series, vol 2, part 4, 

 p. 300. 



This species is very similar in form and plications to 0. subfalcata, 

 Con., of the Virginia Miocene. 



36. o. HEERMANI, Con. Acad. Nat. Sc., Philadelphia. Very irregu- 

 lar in form, thick, ovate and often dilated ; lower valve shallow ; ex- 

 terior very irregular, with large distant angular radiating ribs, and 

 with pits, irregular cavities ; cartilage pit broad and oblique ; upper 

 valve flat or concave, with a profoundly irregular surface. Length 

 5f inches, height 6^ inches. 



Locality. Carrizo creek, Colorado desert. Dr. Heermann. 



