The _C. Gabbii_ will easily be distinguished from any other species yet discovered, from its heavy hinge and enormous lateral teeth. I take great pleasure in dedicating this beautiful fossil to Mr. W. M. Gabb, to whom I am indebted for repeated assistance in my palæontological studies. This species occurs in shelly sands, together with _Tapes regularis_ Gabb and _Murex ponderosus_ Gabb, two other extinct species. The specimens are in the collection of Mr. W. M. Gabb and my own. OSTREA L. _O. Bourgeoisii_ Rémond. The description is from two lower valves, from the collections of Mr. l’Abbé Bourgeois (Pont-Levoy, France) and Mr. Pioche, (San Francisco.) Shell sub-oval, higher than long, strongly contracted near the cardinal area, sub-rounded on the ventral margin; inferior valve comparatively thin, convex, irregular exteriorly, with remote, somewhat rugose, plaits of growth. Ligament fosset long, profound, minutely wrinkled and finely striated, oblique and turned downwards; muscular impression very large, oblique, and sub-central, somewhat prominent. Locality: vicinity of Kirker’s Pass, from a late tertiary bed. I dedicate this new species to Mr. Bourgeois, Professor of Natural History at the School of Pont-Levoy, (Loir-et-Cher, France) who was my first teacher in geology. Description of two Species of Scutella. BY AUGUSTE RÉMOND. SCUTELLA Lam. _S. Gibbsii_ Rémond. Disk oblong-sub-oval, rounded before and truncated behind, posteriorly convex above, slightly depressed in front; inferior surface flat, somewhat concave about the mouth. Apex about midway between the center and posterior margin; ambulacral star non-symmetrical; petals unequal, open at their extremities. Anterior petal straight, longer than the others; the lateral ones nearly straight, diverging from the apex with an angle of about eighty degrees; posterior petals very short, sub-oval, having the anterior side most curved. Four rows of pores in each petal; the inner pores transverse, the outer ones pointed obliquely inwards. Mouth posteriorly sub-central; anal-aperture small, submarginal. Ambulacral furrows double, nearly symmetrical, slightly ramified. Each ambulacral and inter-ambulacral space is occupied by two rows of irregular plates, either pentagonal or hexagonal. Tubercles numerous, crowded in the ambulacral furrows, but much worn off in the specimens examined. Locality: Kern Lake, Buena Vista County. The specimens described are in the collection of the Academy; they were found by Dr. Gibbs, to whom the species is dedicated.