1469 



There are about twenty-five nominal species in our Eocene, a number which 

 abundant material when gathered will afford means of considerably reducing. 

 But six are known in the Oligocene and seven in the Neocene, the recent fauna 

 comprising only three. The different horizons show with great uniformity two 

 species each of Crassinella, three being known from the Atlantic and two from 

 the Pacific American coast in the existing fauna. 



In the Eocene C. alceformis Conrad, 1830 (-f- C. capricranium Rogers, 

 1839, and C. declivis Heilprin, 1881), is the precursor of the Miocene Scam- 

 bulas. A group of nominal species, several of which may prove to be forms 

 of one specific type, contains C. antestriatus Gabb, 1860; C. aquianus Clark, 

 Oct., 1895; C. Halei Harris, 1897; C. sepulcollis Harris, 1896; C. texanus 

 Heilprin, 1890; C. trapaquarus Harris, April, 1895; C. Gabbi Safford, 1864 

 (= C. pteropsis Gabb, Mar., 1860, not of Conrad, Feb., 1860), and C. mac- 

 tropsis Conrad, 1854 (as Gratelupia, -\- antillarum Gabb, 1873, non Reeve, 

 1842, -|- C. Reevei Gabb, 1873); C. carolinensis Conrad, 1875; C. palmulus 

 Conrad, 1846; C. rhomboideus Conrad, 1865 (not of D'Archiac, 1840), and 

 C. obliquatus Whitfield, 1885, are ill-defined or doubtful Eocene forms de- 

 scribed from fragments or internal casts. C. altus Conrad, 1832 (-f- C. curtus 

 Conrad, 1862, described from a young valve with a wrong locality, the type 

 being in the National Collection), a noble species from the Claibornian, first 

 appears in the lower Claibornian of Texas, where it has been named C. texalta 

 by Harris, 1895, and continues to the summit of the Vicksburgian, a very per- 

 fect cast having been obtained from Ocala, Florida, by Mr. Willcox. C. 

 tumidulus Whitfield, 1865, from the Eocene of Alabama, is of somewhat the 

 same type. Of a different form, elongated and carinate with numerous con- 

 centric ripples, are C. protextus Conrad, 1832, the commonest of the Claiborne 

 species; C. ftexurus Conrad, 1858 (-f C. productus Conrad, 1862), from the 

 Jacksonian, and C. littoralis Conrad, 1869, a little known form from Shark 

 River, New Jersey. 



From the Pacific coast come C. grandis Gabb, 1864 (+ C. altus Conrad, 

 1855, not of Conrad, 1832) ; C. compactus Gabb, 1868; C. uniodes Stanton, 

 1896, and the dubious C. uvasanus Conrad, 1855. 



The outline of most of the species is quite variable, as the figures of C. 

 densus in this volume illustrate, and the extension of the concentric sculpture 

 over the disk varies also. One of the most characteristic features of the several 

 species lies in the sculpture of the nepionic shell at and near the umbones of 

 the adult. This may occasionally be absent or obsolete, but when present, as 

 it generally is, is very constant. 



