1855.] 269 



NEITHEA, Drouet. 

 / 



Neithea occidentalism Ovato-triangular, angulated; lower valve inflated, 

 unequally ribbed and concentrically lined, lines very fine; large ribs five, 

 rounded and elevated; smaller ribs equal, two in number in each of the intervals 

 between the larger ribs, which latter have on each side a raised line or fine rib, 

 giving it a trifid character; right valve flat, subconcave. 



Pecten quadricostatus, var. Roemer. Kreid von Texas, p. 64, pi. 8, fig. 4. 



This species differs from N. guadricostata in having but two equal ribs 

 between the larger ones, whilst that species has three corresponding ribs, and 

 it is also proportionally a narrower or more elevated shell. There is quite as 

 much difference between the two as between N. qnadricostata and N. quinque- 

 costata,. 



MACTRA, Lin. 



Mactra Texana. Triangular, ventricose, subequilateral ; anterior extremity 

 subangulated and slightly produced, much above the line of the base, which is 

 regularly and profoundly curved; posterior margin obliquely truncated, ex- 

 tremity angulated ; anterior margin straight and very oblique ; umbo prominent. 



Locality. Prairie between Laredo and Rio Grande City, Texas. 



This species occurs only in casts, and is placed with doubt among the cre- 

 taceous fossils. 



EXOGYRA, Say. 



1. E. fragosa. Orbicular, lower valve ventricose posteriorly, flattened an- 

 teriorly ; ribs very large, prominent, irregular, some of them bifurcated ; umbo 

 not prominent, small, flattened, inner margin rugose-striate. Differs from E. 

 ponder osa, Roem., in its large ribs, small umbo, &c. 



Locality. Between El Paso and Frontera. Major Emory. 



2. E. fimhriata. Upper valve. Very thick, profoundly convex, with ten or 

 twelve distant concentric imbricated lamina. 



T Locality. Texas. Major Emory. 



Tertiary Species. 



O. contracta. Subfalcate, elongated; cavity shallow and remarkably contracted 

 near the hinge. Length nearly two feet. 



Locality. Oyster point, near Mier, Mexico. 



Description o f a Nevj Species of Melania. 

 By T. A. Conrad. 



Melania exigua. Turrited ; volutions 8, disposed to be angulated and some- 

 what scalariform above, cancellated, longitudinal lines wanting on the lower 

 half of the body whorl ; columella reflected ; aperture elliptical. Length one- 

 fifth of an inch. 



Locality. Colorado desert, California. Dr. Le Conte. 



The specimens are numerous and of a chalky whiteness, showing that they 

 are all dead shells. Said to have been found one hundred and twenty miles 

 distant from any stream passed in the route. 1 am indebted to Dr. Caspar 

 Parkinson and Mr. Mactier for specimens. 



